•tamr-^H  hp'oi" 


^^^SITV^CCAUPO^,^ 


AT 


ELEMENTARY 
PHYSICAL   GEOGRAPHY 


elementary 
Physical  Geography 

AN   OUTLINE   OF   PHYSIOGRAPHY 


BY 

JACQUES    W.    REDWAY 


The  waste  of  the  Old  Land  is  the  material  of  the  New ' 


NEW  YORK 

CHARLES    SCRIBNER'S   SONS 

1901 


COPTRIGHT,   1900  BY 

JACQUES    W.    REDWAY 


:^32G 


cvi 


Q353 


PREFACE 


The  science  of  Geogmpliy  sets  forth  the  relations  of  life 
S^      aud  its  environment  to  the  earth,  and  it  is  the  function  of 
both  the  writer  and  the  teacher  of  geography  to  explain 
these  relations.     In  the   Elementary  Natural  Geography 
"P       the  pupil  studies  the  various  peoples  of  the  earth  and  the 
)y        countries  in   Avhich  they  live  ;   in  the  Advanced  Geogi-a- 
N         phy   there   is    presented   in  addition  a  discussion  of   the 
industries  of  life  and  their  geographic  distribution.     In  the 
present  volume,  which  the  author  has  prepared  as  a  log- 
ical sequel,  it  is  designed  to  show  that  the  distribution  of 
i         life   is  governed  very  largely  by  the  conditions  of  geo- 
9>        graphic  environment,  and  that  human  history  and  indus- 
tries are  always  chjsel}^   connected  with  geographic  laws 
— in  many  instances  the  direct  resultants  of  them. 

The  science  of  Geography  as  now  understood  includes 
something  more  than  a  mere  description  of  topographic 
forms — it  comprehends  the  gradual  and  progressive  devel- 
opment of  these  forms  and  their  results  as  regards  life,  as 
well.  It  includes  also  the  effects  of  temperature  and 
moisture,  for  life  and  its  activities  depend  also  on  them. 
That  is,  it  naturally  involves  the  principles  of  Descriptive 
Geography,  Physiogi-aphy,  aud  Economics ;  and  the  pres- 
ent volume  is  designed  to  show  their  interrelation. 

In  scope  this  bo(jk  contains  all  the  principles  recom- 
mended by  the  Committee  of  Fifteen,  and  such  other  feat- 
ures as  have  suggested  themselves  to  th(^  author.  It  is 
designed    to    be  used  in  the  junior  grades  of    the    High 

V 


vi  PREFACE 

School,  and  in  Normal  Schools.  With  judgment  in  the  se- 
lection of  the  topics,  it  may  be  begun  in  the  last  half  of 
the  eighth  year  of  the  Grammar  School.  The  arrange- 
ment of  the  subjects  is  logical,  but  the -teacher  may  readily 
organize  a  course  of  study  in  the  subject  without  reference 
to  the  present  arrangement.  To  make  this  more  easily 
accomplished,  the  principles  of  the  subject  are  set  forth  in 
the  larger  type  ;  relevant  matter  that  is  illustrative  but 
non-essential  is  confined  to  the  notes.  In  general,  the 
teacher  should  not  hesitate  to  omit  a  topic  the  discussion 
of  which  is  too  difficult  for  the  class. 

The  Questions  and  Exercises  are  designed  to  stimulate 
observation  and  independent  thought.  If,  occasionally, 
they  leave  the  pupil  in  doubt,  the  design  of  the  author  will 
be  fulfilled.  The  pupil  must  learn  by  experience  that 
knowledge  does  not  come  in  cut-aiid  dried  ])fickages. 

In  the  preparation  of  the  work  the  author  takes  pleasure 
in  acknowledging  the  material  assistance  of  Miss  Frances 
Bronson,  and  of  his  daughter,  Miss  Elizabeth  Ebert  Eed- 
way.  But  to  more  than  anyone  else,  however,  thanks  are 
due  to  Miss  Stella  Wilson,  Instructor  in  Physical  Geog- 
raphy in  the  Central  High  School,  Columbus,  Ohio.  To 
Miss  Wilson's  keen  judgment,  excellent  criticism,  and  ex- 
perience are  largely  due  the  usefulness  as  a  text-book  which 
this  volume  may  have. 

The  books  designated  for  reference  and  collateral  read- 
ing are  intentionally  few  in  number,  and  those  most  com- 
monly cited  should  be  in  the  school  library.  The  teacher 
will  also  find  it  very  advisable  to  get  in  close  touch  with 
the  United  States  Geological  Survey  and  the  Weather 
Bureau.  The  Bureau  of  Geography  recently  established 
at  Winona,  Minn.,  will  also  be  helpful. 

J.  W.  R. 


CONTENTS 


PAGE 

Introdttctort, 1 

CHAPTER 

I.  The  Earth  Among  Planets    ......       9 

II.  The  Structure  of  the  Earth        .         .         .         .         .20 

III.  Land  and  Water,  and  their  Outlines  .         .         .41 

IV.  The    Results    op     Slow    Movements    of    the    Rock 

Envelope  :  Plains,  Plateaus,  and  Mountains  .         .     56 

V.  Destructive  Movements  of  the  Rock  Envelope  :  Vol- 
canoes AND  their  Phenomena     .         .         .         .         .80 

VI.  Destructive     Movements    of    the    Rock     Envelope  : 

Earthquakes       ........     95 

VII.  The  Wasting  of  the  Land  :    The  Work  of  Rivers      .  105 

VIII.  The  Wasting  of  the  Land  :    The  Work    of    Under- 
ground Waters  .         .        .        .         .         •        •         .132 

IX.  The    Wasting    of    the    Land  :    The    Work    op    Ava- 
lanches AND  Glaciers 150 

X.  The  Wasting  of  the  Land:  The  Results  of  Im- 
perfect Drainage  and  Obstructed  Lakes  and 
Marshes 1^5 

XI.  Ocean  Waters  and  THEra  Movements:    Waves,  Tides, 

AND  Currents 1^^ 

XII.  The  Atmosphere  and  its  Properties  :  Winds       .         .  214 

XIII.  The    Moisture    of    the   Atmosphere:    Seasonal    and 

Periodk!AL  Distriiuttion  of  Rainfall         .         .         .  231 


viii  CONTENTS 

CHAPTER  PAGE 

XIV.  The  Moisture  of  the  Atmosphere  :    Cyclonic  Storms  248 

XV.  Electricali  and  Luminous  Phenomena  of  the  Atmos- 
phere   268 

XVI.  Climate  and  its  Factors 287 

XVir.  The  Dispersal  op  Life 303 

XVril.  Geographic  Distribution  of  Plants  and  Animals       .  315 

XIX.  Man 335 

XX.  The  Industrial  Regions  of  the  United  States  .  352 

Appendix     ...........  375 

Index ,         .  381 


LIST   OF   MAPS    AND   PLATES 


The  Solar  System  (Colored)  . 

Photograph  of  Moon 

Order  of  Strata 

North  America  in  ARCHiEAN  Times 

North  America  in  Cenozoic  Era 

United  States  in  Quaternary  Age 

Land  and  Water  Hemispheres 

Elevation  of  Land  and  Depth  of  Oceans  (Colored) 

Stretch  of  Norway  Coast 

Barrier  Beaches  of  Carolina  Coast 

Plateaus  of  the  Colorado  River  . 

Distribution  of  Volcanoes  (Colored) 

Loops  and  Cut-offs  of  the  Louver  Mississip 

Palmyra  Bevel,  Mississippi  Rh'er  . 

Delta  of  the  Mississippi  River 

Chesapeake  Bay— A  "Drowned"  Valley 

Old  Stream-bi:ds  of  the   Tuolumne  River 

RivEis  Systems  and  Drainage  (Colored) 

Glaciated  RE(iioN  of  the  United  States 

]\Iarsh  Lakes  of  Florida 

Lagoons  of  Marthas  Vineyard 


PAGE 
.        10 

.        11 

.  33 
.  34 
.  35 
.  36 
.  40 
44,  45 
.  46 
.  52 
.  63 
.  92 
.  108 
.  110 
.  116 
.  117 
122 
130,  131 
.  159 
.  166 
.  168 


LIST   OF   MAPS   AND   PLATES 


Lake  St.  Clair         ...... 

Lake  Bonneville  and  its  Remnants 
Section  Along  the  Great  Lakes    . 
Chart  of  Co-Tidal  Lines         .         .         ,         . 
Ocean  Currents  (Colored)       .... 

Prevailing  Winds  of  the  Atlantic 

Chart  of  Winds  (Colored)      .... 

Distbibution  of  Rain  (Colored) 

Storm  Maps — First  and  Second  Days  (Colored) 

Chart  of  Magnetic  Isogonics  .... 

Isotherms- January  and  July  (Colored) 
Distribution  of  Animals  (Colored) 
Distribution  of  Vegetation  (Colored)    . 
Races  op  Man  (Colored)  .... 

Physical  Map  of  the  United  States  (Colored) 
New  York  Harbor  and  its  Approaches  (Colored) 


PAGE 

.  173 

.  174 

,  176 

.  199 

.  201 

.  218 

.  221 

.  239 

.  260 

.  274 

.  292 

.  318 

.  325 

.  339 

.  353 

.  369 


PHYSICAL  GEOGRAPHY 


INTRODUCTORY 

OxLY  a  casual  tlionglit  is  needed  to  make  it  apparent 
that  life  ou  the  eartb,  as  we  now  find  it,  depends  on  a  very 
delicate  adjustment  to  its  surroundings.  Living  beings 
require  certain  conditions  of  heat,  moisture,  and  geo- 
graphic environment;  and  if  tliese  are  changed  ever  so 
slightly  the  life  forms  must  adjust  themselves  to  the  new 
conditions,  or  else  they  must  seek  a  new  abiding-place; 
or,  j)erhaps,  they  may  perish  altogether. 

For  instance,  turf  grass  requires  water  at  very  short 
intervals,  and  if  for  several  successive  years  there  are 
droughts  of  five  or  six  months'  duiation,  it  will  die.  And 
if  there  are  herds  of  cattle  in  the  region,  thej^  nmst  adjust 
themselves  to  the  changed  conditions.  They  must  adapt 
themselves  to  other  food,  or  the}'  must  migrate.  Other- 
wise the}'  too  will  perish. 

Were  the  temperature  of  the  earth  to  change  only  a  few 
degrees  there  would  be  a  similar  disturbance  that  would 
involve  almost  every  living  thing.  And  if  it  should  fall  so 
low  that  the  water  were  everywhere  frozen,  life  as  we  now 
know  it  could  not  exist  any  great  length  of  time,  because 
living  beings  need  in  their  structure  a  large  proportion  of 
water,  and  the  latter  must  be  taken  into  the  structure  in 
a  liquid  form.  For  a  similar  reason,  if  all  the  water  were 
in  the  form  of  vapor,  life  could  not  long  endure  unless  the 

1 


2 


PHYSICAL   GEOGKAPHY 


life  forms  were  very  different  in  structure  from  those  with 
Avhicli  we  are  acquainted. 

Life  is  by  no  means  evenly  distributed  over  the  earth, 
however.  A  few  species  spend  the  greater  part  of  their 
existence  in  the  air,  and  a  larger  number  live  in  Avater  only. 
By  far  the  greater  number  of  species,  however,  live  at  the 
plane  of  contact  between  the  atmosphere  and  the  earth's 


A    t-hKllLE   VALLliV,   NhW    VuKK 
Cipabk  of  producing  nhiiiidniit  food -stuffs,  and  densely  peopled. 

rock  envelope — that  is,  on  the  land  surface  of  the  earth. 
Their  distribution  is  governed  by  the  conditions  of  warmth, 
moisture,  and  surface,  and  if  these  conditions  were  to 
change  ever  so  slightly,  the  distribution  would  be  disturbed. 
Life  and  its  distribution  are  governed  by  geographic  laws ; 
if  the  latter  change,  so  must  the  former. 

Man,  who  stands  at  the  head  of  animate  nature,  is  able 
to  endure  a  much  wider  range  of  warmth,  moisture,  and 


INTRODUCTORY  3 

surface  features  than  most  other  living  beings.  He  can 
withstand  extremes  of  heat  and  cold  that  are  fatal  to  most 
other  animals,  and  he  can  live  indifferently  in  places  of 
great  drought  or  of  excessive  moisture.  The  arctic  re- 
gions are  not  so  cold,  nor  the  tropical  lands  so  hot  that 
man  cannot  dwell  there ;  and  throughout  the  wide  world 
one  can  find  scarcely'  an  ice-clad  summit  or  a  sun-beaten 
desert  in  which  human  beings  have  not  lived. 

On  account  of  these  varying  conditions — all  the  result  of 
geographic  laws — the  study  of  the  earth  is  both  important 
and  interesting,  because  it  is  the  home  of  man.  Like  all 
forms  of  life,  man  requires  food  ;  more  than  any  other  ani- 
mal, he  needs  shelter.  His  food,  of  which  he  consumes 
about  eighty  tons  during  the  three  or  four  score  years  of 
his  existence,  comes  from  the  earth — the  land,  the  water, 
and  the  air  each  yielding  part — and  the  materials  that  are 
used  for  clothing  and  shelter  come  also  from  the  same 
source — the  earth. 

So,  in  order  to  understand  the  story  of  life,  its  history 
and  its  industries,  one  must  learn  about  the  physical  geog- 
raphy of  its  surroundings — that  is,  about  its  environment, 
or  the  various  conditions  of  heat,  moisture,  and  surface 
features.  Land  animals  could  not  live  until  the  waters 
were  separated  from  the  land.  Before  they  could  main- 
tain life,  vegetation  must  have  spread  itself  over  the  land  ; 
and  before  vegetation  could  endure  there  must  have  been 
soil.  And  before  there  could  be  soil,  the  surface  of  the 
land  must  have  been  folded,  broken,  worn,  and  furrowed, 
so  that  tlui  fragments  of  rock  could  be  ground  fine  and 
formed  inU)  soil.  All  these  earth-weathering  })rocesses 
must  have  been  going  on  before  the  higher  forms  of  life 
could  exist,  and  all  over  the  surface  of  the  land  such 
changes  are  even  now  going  on  from  day  to  day.  Scarcely 
a  summer  shower  falls  that  does  not  leave  its  marks;  and, 


4  PHYSICAL  GEOGRAPHY 

indeed,  tlirougliont  tlie  physical  history  of  the  earth  the 
most  apparent  feature  is  constant  change. 

From  the  time  the  land  was  first  divided  from  the  waters, 
the  continents,  or  great  bodies  of  land  have  been  ever 
changing.  In  places,  alternately  sinking,  rising,  and 
warping  in  various  ways,  the  shore  outlines  have  taken 
various  forms.  Riigged  coasts  sinking  below  sea-level 
have  resulted  in  the  fjorded  shores,  such  as  those  of  the 


ARCTIC   LANDS 

Too  cold  and  not  oioiigh  soil  for  the  support  of  life. 

North  Atlantic  States,  making  the  harbors  where  so  much 
of  the  manufacture  and  commerce  of  the  country  have 
centred.  Rising  coasts  have  lifted  natural  harbors  above 
sea-level,  making  the  approaches  to  the  land  so  difficult 
that  vessels  can  find  no  sheltered  anchorage.  Old  sea- 
bottoms,  covered  with  sediments  that  form  the  richest 
soil,  have  been  lifted  above  the  sea,  and  in  time  have  be- 
come densely  peopled  areas. 


INTRODUCTORY  5 

Certain  forces  are  causing  the  surface  of  the  rock  en- 
velope to  wrinkle  and  fold,  forming  plateaus,  mountains, 
and  valleys  ;  and  at  the  same  time  the  waters  of  the  atmos- 
phere, falling  as  rain  or  snow,  are  constantly  at  work  wear- 
ing away  the  wrinkles  and  folds,  carrying  the  material  back 
to  the  sea. 

It  is  necessary  to  know  about  these  processes,  and  to 
understand  how  they  are  going  on,  because  almost  every 
form  of  life  is  more  or  less  modified  by  them,  and  certainly 
the  history  and  the  industries  of  man  are  very  largely  gov- 
erned by  them.  Man  may  rise  superior  to  his  environ- 
ment— that  is,  his  geographic  surroundings — but  he  is  al- 
ways more  or  less  modified  by  it.  Mountains  and  vallejs, 
plains  and  plateaus,  oceans  and  rivers,  have  all  been  potent 
factors  in  making  the  destiny  of  peoples. 

The  rugged  and  barren  slope  of  Norway  forbade  any 
great  development  of  agriculture,  while  the  deepl}'  fjorded 
shores  invited  the  pursuits  of  the  sea.  The  Norse  people, 
therefore,  became  sea  rovers  and  magnificent  sailors.  The 
uncultivable  mountains  of  Greece  could  not  well  yield  the 
food-stuffs  necessary  for  the  poj^ulation,  so  we  find  a  his- 
tory of  "  Greece  scattered."  From  the  remotest  times  the 
rich  valley  of  the  Tigris  and  Euphrates,  because  of  its  fer- 
tility, has  always  attracted  people,  and  we  therefore  find  it 
a  densely  settled  region. 

Unless  there  is  something  to  unfit  them  for  human  habi- 
tation, lowlands  are  favorite  places  of  dwelling,  and  by  far 
the  greater  part  of  the  world's  population  is  found  in  them. 
How  is  the  statement  borne  out  in  the  case  of  the  Central 
Plain  of  North  AuKuica  ?— the  swampy,  forest  plain  of 
the  Amazon  ? — the  great  lowland  region  of  southeastern 
Asia? — the  northern  plains  of  Eurasia? 

River  bottom-lands,  also,  are  nearly  always  densely  peo- 
l)led.     How  is  this  illustrated  in  the  history  of  Egypt? — 


6  PHYSICAL   GEOGRAPHY 

with  regard  to  the  nations  dwelling  in  the  Mesopotamia 
— the  valley  of  the  Ganges?— the  bottom-lands  of  th( 
Mississippi  Kiver? — the  Sacramento-San  Joaquin  Valley' 
Extensive  desert  regions   are  always   sparsely   peopled 


A    RUGGED   NORWEGIAN   SLOPE 
A  locality  >to!  mitahlc  for  farming  ;  a  few  food-plants  tnav  be  grown. 

why?  How  is  this  illustrated  in  the  eastern  and  west- 
ern halves  of  the  United  States?  The  population  of 
rugged  highlands  and  mountain  ranges  is  usually  sparse ; 
is  there  a  good  reason  therefor  ? 

The  hot  regions  of  the  laud  are  almost  always  densely 
peopled,  the  deserts  and  forest  swamps  excepted.     Is  this 


INTRODUCTORY  7 

true  of  the  intensely  cold  regions?  Life  thrives  best  in 
regions  of  warmth  and  of  strong  sunlight.  Are  all  parts 
of  the  earth  equally  warmed  ?  Have  all  parts  the  same  in- 
tensity of  light?     Compare  the  density  of  population  of 


A   TROPICAL   SCHNE 
Koth  tcmpiiaturr  and  moisturr  arr  favorahli-  lo  n  ^rrat  proiliictivily  of  food -stuffs. 

cold  and  dimly  lighted  parts  of  the  earth  with  that  of  the 
Avarm  and  strongly  lighted  parts:  in  which  is  it  greatest? 

The  study  of  the  distribution  of  heat  and  cold,  of  rain 
and  drought,  of  highlands  and  lowlands,  and  of  fertile^  and 
unfertile  regions  form  an  essential  part  of  the  study  of 
geography  ;  the  study  of  the  progressive  changes  that  have 
been  and  are  now  taking  ])lace  on  the  earth's  surface^  con- 
stitutes the  science  of  physic^graphy,  or  "  nature-writing." 


8  PHYSICAL   GEOGRAPHY 

The  object  of  this  book  is  to  show  that  the  fundamental 
hiws  of  «>eograi)hic  science  not  only  control  the  structure 
of  life  forms  and  their  distribution  over  the  earth,  but  that 
they  also  largely  control  and  modify  the  history,  the  activi- 
ties, and  the  various  economies  of  man,  as  well, 

QUESTIONS  AND  EXERCISES.— What  are  the  leading  industries 
of  the  city  or  town  in  which  you  live  ?  Note  and  describe  a  geographic 
feature  that  favors  any  one  of  these  industries,  and  without  which  the 
industry  could  not  thrive. 

What  would  be  the  effect,  so  far  as  the  habitability  of  the  sur- 
rounding region  is  concerned,  were  the  rainfall  to  be  diminished  one- 
half? 

How  would  a  material  change  in  the  surface  features  affect  the  indus- 
tries ? 

On  p.  369  is  a  map  of  New  York  Harbor  ;  what  would  be  the  effect  on 
the  commerce  of  the  port  if  the  surface  of  the  water  were  lowered  two 
hundred  feet  ? 

Mention  two  or  more  reasons  why  lowland  regions  are  more  densely 
peopled  than  highlands. 

Quito,  the  capital  of  Ecuador,  is  in  the  midst  of  a  fertile  region  nearly 
two  miles  above  sea-level ;  what  are  its  advantages  over  the  coast  plain 
region  to  the  westward  ? 

Make  a  list  of  half-a-dozen  or  more  extensive  regions  that  are  not 
habitable,  and  explain  the  geographic  reasons  for  their  condition. 


COLLATERAL   READING. 

Mill. — Realm  of  Nature,  pp.  331-336. 
Shaler.— Nature  and  Man  in  North  America. 


CHAPTEE  I 

THE  EARTH  AMONG  PLANETS 

The  Solar  System. — The  cluster  of  heavenly  bodies 
called  the  solar  system  is  one  of  a  great  number  of  groups 
in  space.  The  members  of  this  group  revolve  about  a 
common  centre  of  gravity,  however,  and  for  this  reason 
they  are  called  collectively  a  system.  The  number  of 
bodies  composing  it  is  unknown. 

The  members  of  this  system  vary  greatly  in  size.  The 
largest  is  about  886,000  miles  in  diameter,  and  the  small- 
est are  probably  too  minute  to  be  measured  by  ordinary 
standards.  Eight  of  them,  however,  are  three  thousand 
miles,  more  or  less,  in  diameter,  and  a  large  number,  about 
four  hundred,  vary  from  ten  miles  to  less  than  five  hundred 
in  diameter. 

The  largest  member  of  the  solar  system,  the  sun,  is 
about  eight  hundred  times  as  large  as  all  the  others  to- 
gether, and  the  common  centre  of  gravity  around  which 
they  revolve  is  very  near  to  it  or,  perhaps,  within  its  mass. 
The  eight  bodies  next  in  size  are  called  planets,  and  all  but 
two  of  them  are  attended  each  by  one  or  more  satellites  or 
moons.  The  four  hundred  or  more  small  planets  are  called 
asteroids,^  or,  more  properly,  jjlanetoids.  In  addition 
there  are  several  comets  '■*  and  groups  of  meteors  ^  that 
have  a  permanent  place  in  the  solar  system. 

There  is  much  evidence  to  show  that  the  planets  are 
composed  of  the  same  kinds  of  substance  or  material,  but 
it  seems  certain  that  they  are  very  unlike  one  another  in 

9 


10 


PHYSICAL   GEOGRAPHY 


physiccil  condition  ;  for  while  some,  bulk  for  bulk,  are  but 
little  heavier  than  water,  others  are  about  as  lieav}'  as  iron 
ore.  It  seems  certain  also  that  this  difference  is  largely  a 
result  of  temperature ;  for  while  some  of  the  planets  have 


Xeptune 


THE    SOLAR   SYSTEM 
Tkc  space  within  the  orbit  of  Jupiter  sljows  the  relative  sije  of  the  Sun. 

apparently  lost  the  greater  part  of  their  heat,  others  still 
are  very  hot.  The  sun,  for  instance,  is  a  glowing  mass 
surrounded  by  white-hot  vapors,  and  its  heat  is  probably 
greater  than  any  artificial  heat  known. 


THE   EARTH   AMONG    PLANETS 


11 


The  Sun  and  the  Planets. — The  similarity  of  the  sun 
and  the  planets  to  one  another  is  far  more  marked  than 
their  points  of  difterence.  All  whirl  around  a  common 
centre  of  gravity  in  a  direction  from  west  to  east,  and  each 
turns  or  spins  on  its  axis  in  the  same  direction.  Each  is 
nearly  spherical  in  shape,  differing  from   a   sphere  by  a 


A   PORTION  OF   THE   MOON 
From  a  photograph. 

curvature  that  in  nearly  every  instance  is  a  slight  flatten- 
ing at  the  poles  of  their  axes.  Several  are  known  to  be 
suiTOunded  each  with  an  atmosphere,  and  there  is  some 
evidence  that  this  is  true  of  all. 

It  is  now  generally  l>elieved  that  the  members  of  the 
solar  system  formerly  existed  as  a  body  of  gaseous  matter  ;' 
because   the  force  of  gravity  drew  the  particles  together, 


12  PHYSICAL   GEOGKAPHY 

toward  the  ceutre  of  gravity,  a  rotation  of  the  mass  around 
the  centre  of  gravity  resulted.  Finally,  parts  of  the  mass 
were  thrown  off,  one  after  another,  forming  the  planets. 
In  the  same  manner,  tlie  rapid  rotation  of  each  planet 
threw  off  portions  of  its  mass  forming  the  satellites. 

Although  the  assumed  formation  of  the  solar  system  by 
this  process  is  a  matter  of  theory,  it  is  a  theory  supported 
by  evidence.  The  telescope  reveals  many  such  masses  of 
gaseous  matter  showing  planetary  formation.  The  spec- 
troscope, an  instrument  for  analyzing  light,  shows,  not 
only  the  matter  of  which  they  are  composed,  but  also  that 
the  matter  is  in  rapid  motion.  It  shows  also  that  the 
earth  and  the  sun  contain  the  same  kinds  of  matter.  Cal- 
cium, hydrogen,  iron,  and  sodium,  the  substances  of  greatest 
abandance  at  the  surface  of  the  sun,  are  also  among  the 
most  abundant  substances  in  the  composition  of  the  earth. 
"^  The  Form  of  the  Earth. — The  earth  is  one  of  the 
planets.  From  Table  I.  {Appendix),  find  how  it  ranks 
among  the  other  planets  in  size  ; — in  distance  from  the  sun. 
In  form  the  earth  resembles  the  other  planets,  being  nearly 
spherical,  but  slightly  flattened  at  the  poles.  It  is  usually 
said  to  be  an  oblate  spheroid — that  is,  a  sphere  flattened 
at  its  polar  diameter,  but  it  deviates  slightly  from  this 
form  ;  hence  the  term  geoid  is  sometimes  used  to  apply  to 
its  irregular  shape. 

The  spherical  form  of  the  earth  is  shown  in  various 
ways  that  are  well  known,  but  it  is  demonstrated  most 
clearly  by  surveying  a  horizontal  straight  line  along  a  level 
surface,  such  as  that  of  a  jjond.^  The  line  thus  projected 
does  not  lie  parallel  to  the  surface  ;  the  latter  recedes  or 
curves  away  from  it,  and  the  curvature  is  such  as  corre- 
sponds to  the  surface  of  a  spherical  body. 

Were  the  earth  a  true  sphere,  the  weight  of  a  body 
would  be  the  same  at  every  part  of  its  surface.     There  is 


THE   EARTH  AMONG   PLANETS  13 

a  lueasnrable  difference,  however/'  and  it  is  foimd  that  a 
given  body  weii^hs  a  little  more  in  i>olar  than  in  equatorial 
latitudes,  and  from  the  careful  experiments  based  on  this 
fact  tlie  amount  of  Hatteniug  at  the  poles  has  been  deter- 
mined. 

The  following  are  its  dimensions  : 

Polar  diameter 7,901.5  miles 

Equatorial  diameter 7,926.6  miles 

Cireumferenee  at  equator 24,912  2  miles 

Suri'aee  (approximate) 197,000,000  square  miles 

What  is  the  dilierence  between  the  polar  and  the  equa- 
torial diameter?  On  a  globe  one  foot  in  diameter  the  dif- 
ference would  be  what  part  of  one  inch  ?  Compare  the 
diameter  of  the  earth  with  that  of  the  sun  (Table  I.,  Jjj- 
peudix).  Large  as  the  earth  seems  to  us,  it  would  require 
about  one  and  a  quarter  million  bodies  of  its  size  to 
niakt!  a  globe  as  large  as  the  sun. 

Motions.— The  earth  has  several  distinct  motions.  It 
revolves  about  the  common  centre  of  gravity  in  an  ellipti- 
cal path,  making  a  complete  journey  in  very  nearly  8()5i 
days — a  })eriod  of  time  called  a  yeaj-.  It  also  rotates,  or 
spins  on  its  axis.  The  time  required  to  make  a  complete 
rotation  is  called  a  dai/  and  is  commoidy  used  as  a  unit  for 
the  measurement  of  short  intervals  of  time.  The  poles  of  the 
earth  also  move  or  oscillate  in  a  nearly  circular  i)ath.  The 
motion  resembles  that  of  the  poles  of  a  "  sleeping  "  top. 

Th<;  first  motion  combined  with  the  inclination  of  the 
axis  giv(!S  rise  to  the  successive  change  of  the  seasons  and 
tht!  varying  hsngth  of  sunshine  and  darkness.  The  second 
motion  causes  tin;  succession  of  day  and  night ;  it  is  "day" 
in  all  ]);iits  of  the  surface  turiUHl  toward  the  sun  and 
"  nigiit  "  on  tlie  opposite  side.  The  third  motion  causes  the 
[)lienomcnon  or  movement  commonly  known   as  the  ^/yc- 


14 


PHYSICAL   GEOGKAPHY 


cessio?}  of  t/w  equinoxes.  In  long  intervals  of  time  it  is 
thought  that  this  motion  is  connected  with  certain  changes 
of  climate.  It  is  a  subject,  hoAvever,  that  belongs  to  the 
science  of  astronomy,  and  not  to  physical  geography. 

Effects  of  the  Inclination  of  the  Axis. — The  axis  of 
the  earth  is  not  peipendicular  to  the  earth's  path  (called 
i\\e  l^lane  of  the  ecliptic),  but  inclines  about  23|^  degrees,  as 
shown  in  the  accompanying  ligure.  In  long  intervals  of 
time  the  amount  of  inclination  varies.  Practically,  how- 
ever, the  axis  points  ahvays  in  the  same  direction  and 
therefore  is  said  to  be  parallel  to  itself.  The  northern  end 
of  the  axis  prolonged  would  extend  nearly  in  the  direction 
of  a  star  named  Polaris  ;  this  star  is  therefore  often  called 
the  north  star. 

If  the  earth's  axis  were  perpendicular  to  the  plane  of  its 
orbit,  each  place  would  have  the  same  unvarying  season. 


INCLINATION   OF  THE    EARTHS   AXIS 
The  unshaded  hemisphere  shows  the  position  of  the  light  circle  at  each  of  the  four  seasons. 


It  would  be  hot  in  equatorial  regions,  mild  in  mid-lati- 
tudes, and  cold  in  polar  regions,  the  intensity  of  heat  in- 
creasing from  the  poles  toward  the  equator. 


THE   EARTH  A.MOXG    PLANETS  15 

With  the  axis  inclined,  however,  the  case  is  different. 
An  inspection  of  the  accompanying  diagram  shows  that 
during  the  month  of  June  the  sun's  rays  fall  almost  verti- 
cally on  mid -latitude  parts  of  the  Northern  Hemisphere, 
while  iu  the  corresponding  latitudes  of  the  Southern 
Hemisphere  the  rays  are  very  oblique.  At  this  season, 
therefore  the  Northern  Hemisphere  receives  more  light 
and  more  heat  than  the  Southern. 

Six  mouths  later  the  conditions  are  reversed;  the  belt 
of  vertical  and  nearly  vertical  rays  is  in  the  Southern  Hem- 
isphere, while  in  the  Northern,  the  rays  of  light  nnd  heat 
are  very  oblique.  At  this  season,  therefore,  the  Southern 
Hemisphere  receives  its  greatest  Warmth.  Thus,  it  is  seen, 
the  amount  of  light  and  warmth  received  by  each  hemi- 
sphere varies.  In  equatorial  latitudes  the  difference  is  not 
great,  but  beyond  the  tropics,  in  higher  latitudes,  it  is  the 
ditierence  between  winter  and  summer.  In  polar  latitudes 
the  sun  is  shining  the  greater  part  of  the  time  for  six 
months  alternately  in  each  hemisphere,  the  other  hemi- 
sphere being  in  darkness.  As  a  result  the  season  of  sun- 
shine, or  summer,  becomes  oppressively  hot  at  times,  while 
the  season  of  darkness,  or  winter,  is  intensely  cold. 

The  rotation  or  spinning  of  the  earth  on  its  axis  causes 
the  succession  of  day-light  and  darkness,  or,  popularly, 
"  day  "  and  "  night."  One-half  the  surface,  being  always 
toward  the  sun,  is  therefore  illuminated,  while  the  opposite 
side  is  in  darkness.  The  rotation  of  the  earth,  however, 
pn'S(;iits  every  ])art  successively  toward  the  sun,  lighting 
all  paits  in  turn.  AVere  the  axis  of  the  earth  perpendicu- 
lar to  the  direction  of  the  light-rays,  day  and  night  would 
be  of  equal  duration  in  all  parts  of  the  earth's  surface ;  but 
on  account  of  its  inclination,  the  relative  length  varies,  not 
only  in  diflerent  latitudes,  but  with  the  changes  of  the 
seasons  in  the  same  latitude. 


16 


PlTYSrCAL   GEOGRAPHY 


In  the  tonitl  zone  the  period  of  daylight  and  darkness 
does  not  vary  much  from  twelve  hours  each,  and  at  the 
equator  each  is  twelve  hours  long  through  the  year.  In  the 
temperate  zones  the  daj's  are  longest  near  the  polar  circles 
and  shortest  near  the  tropics,  varying  from  thirteen  to 
twenty-four  hours.  Within  the  frigid  zone  day  and  night 
correspond  practically  to  summer  and  winter.  There,  both 
the    day    and   the   night  vary  from  a  few  brief  moments 

to  six  months  in  length. 
The  relative  length  of 
daylight  and  darkness  and 
the  changes  of  the  sea- 
sons have  much  to  do  with 
the  subject  of  physiogra- 
phy. For  their  vitality 
almost  all  the  forms  of 
life  depend  not  only  on 
the  presence  of  sunlight, 
but  on  the  time  and  man- 
ner of  distribution  as  well. 
Only  a  very  few  species 
of  animals  and  plants 
thrive  in  regions  of  long- 
fteieVg%''lftt\iay.''"^^^^  coutinued   darkncss,  and 

they  are  mainly  the  lower 
forms;  the  higher  species  require  an  environment  in  which 
light  and  darkness  follow  one  after  the  other  in  periods  of 
short  duration.  With  few  excej)tious,  plants  fail  to  mature 
and  fructify  unless  exposed  to  strong  light,  and  many  spe- 
cies will  not  live  at  all.  Plants  that  are  forced  into  blos- 
som in  darkened  rooms  have  usually  pale  or  white  flowers, 
and  the  leaves  of  growing  plants  are  apt  to  be  yellow 
instead  of  green. 


RELATIVE  LENGTH  OF  DAY  AND  NIGHT 
The  shaded  part  of  each  parallel  ihows  the  length 


THE   EARTH  AMONG   PLANETS  17 

QUESTIONS  AND  EXERCISES.— Make  a  circle  one  inch  in  diam- 
eter on  the  blackboard,  and  from  the  centre  of  this  circle,  with  a  ra- 
dius fifty-five  inches  long,  draw  as  much  of  the  arc  of  a  circle  as  the 
size  of  the  blackboard  will  permit.  The  two  circles  represent  the 
relative  size  of  the  earth  and  the  sun. 

In  the  diagram,  p.  14,  the  axis  of  the  earth  is  inclined  23^  degrees 
from  the  dotted  line ;  which  of  these  positions  represents  summer 
in  the  Northern  Hemisphere  ?— In  the  Southern  ?  Copy  the  diagram, 
p.  16,  and  mark  the  point  the  sun's  rays  reach  beyond  the  north 
pole  ;  how  many  degrees  from  the  pole  to  this  point  ?  What  circle 
passes  through  this  point  ?  Mark  the  point  on  the  circumference 
where  the  rays  are  vertical.  What  circle  passes  through  this  point  ? 
From  each  pole  to  the  equator  the  angular  distance  is  ninety  degrees  : 
find  the  distance  in  degrees  from  the  Arctic  Circle  to  the  Tropic  of 
Cancer  ;  this  distance  is  the  width  of  the  Temperate  Zone.  If  the  in- 
clination of  axis  were  28  degrees,  what  would  be  the  width  of  each 
light-zone  ?  If  32  degrees  ?  Ninety  degrees  less  twice  the  angle  of  in- 
clination equals  the  width  of  the  Temperate  Zone. 

In  the  diagram,  p.  16,  the  proportionate  length  of  the  longest  day  and 
shortest  night  are  shown  by  the  shading  :  determine  by  measurement 
the  length  of  the  longest  day  in  latitude  40  ;  in  latitude  60  .  Sub- 
di'vt'de  the  parallel  into  tnventy-four  parts  by  halving  it  three  times  and 
di'vidinp  the  last  subdi'visions  each  into  three  parts  ;  each  of  the  smallest 
subdi<visions  has  practically  an  hour  lvalue. 

COLLATERAL   READING  AND   REFERENCE. 

Mill. — Realm  of  Nature,  pp.  63-81. 

Redway. — Manual  of  Geography,  pp.  64-78. 

Howe. — f^leinents  of  Asti-onomy.     Problems,  a-g,  p.  83. 

Jackson.  — Astronomical  Geography. 

NOTES 

*  The  asteroids  move  in  orbits  in  the  space  between  Mars  and 
Jiil)iter.  Many  of  them  do  not  exceed  twenty  or  thirty  miles  in 
diameter,  and  the  largest  [)robably  does  not  exceed  live  hundred 
miles.  Their  combined  volume  is  less  than  one  four-thousandth 
I)art  of  the  mass  of  the  earth.  Eros,  one  of  the  recently  discov- 
ered asteroids,  has  an  orbit  so  eccentric  that  it  crosses  that  of 
Mars,  and  at  times  is  nearer  to  the  earth  tlian  is  Mars. 


18  PHYSICAL   GEOGRAPHY 

^  But  little  is  known  about  the  nature  and  structure  of 
comets,  but  it  is  thought  that  the  chief  part  of  their  masses,  in 
most  instances,  is  gaseous  matter.  One  comet,  Tempel's,  un- 
doubtedly consists  of  a  vast  swarm  of  meteors,  but  it  is  probable 
that  the  various  couiets  are  differently  constituted.  Several  of 
them  belong  to  the  solar  system,  but  many  are  temporary  visitors, 
coming  from  unknown  regions  of  space,  whirling  around  the  sun 
and  again  vanishing. 

^  Meteors,  or  shooting  stars,  are  small  bodies  that  seem  to  ex- 
ist very  generally  through(jut  space.  In  a  few  instances  they  are 
seen  in  clusters,  as  in  the  case  of  Tempel's  comet.  The  earth, 
and  probably  the  other  planets,  encounter  many  thousands  of 
them  daily,  in  sweeping  through  space.  By  far  the  greater  num- 
ber on  reaching  the  earth's  atmosphere  are  heated  to  whiteness — 
partly  by  compression  of  the  atmosphere  in  front  of  it,  and 
partly  by  friction  against  it— and  are  dissipated  as  white-hot 
vapor.  Some  of  the  larger  ones  reach  the  earth,  and  many  of 
these  have  been  analyzed.  Some  consist  mainly  of  iron  and 
nickel  in  a  metallic  form  ;  others  are  composed  of  matter  not 
differing  materially  from  lavas.  No  element  has  yet  been  found 
in  a  meteor  that  does  not  occur  in  the  earth,  but  in  a  few  in- 
stances chemical  compounds,  of  iron,  nickel,  and  phosphorus, 
and  certain  crystalline  forms,  have  been  found  in  meteors  that 
have  never  been  met  with  naturally  in  terrestrial  substances.  In 
one  instance  gold,  in  another  diamonds,  were  found  in  a  mete- 
orite. 

*  So  far  as  is  known,  matter  exists  in  three  physical  forms — 
solid,  liquid,  and  gaseous— and  nearly  every  chemical  element 
and  many  of  their  compounds  may  assume  each  form.  In  the 
solid  form  the  molecules  are  bound  by  a  strong  cohesion  ;  in  the 
liquid  form  they  are  very  slightly  cohesive  ;  in  the  gaseous  form 
they  strongly  repel  one  another.  Most  of  the  substances  that  in 
the  earth  are  solids,  in  the  sun  exist  as  white-hot  vapors. 

5  An  interesting  experiment  is  suggested  by  Professor  Edward 
Jackson  (Astronomical  Geography,  p.  3).  Three  stakes  are  in 
line,  or  as  nearly  in  line  as  is  practicable,  one  mile  apart,  along 
the  shore  of  a  canal  or  a  pond.  On  these,  sighting  marks  are  made 
at  a  uniform  distance  above  water-level.  An  engineer's  level  is 
then  placed  so  that  the  cross-wires  cut  the  sighting  marks  of  the 
first  and  third  stakes.     If  the  telescope  of  the  level  be  turned 


THE   EARTH   AMONG   PLANETS 


19 


upon  the  middle  stake  it  will  be  found  that  the  cross-wires  cut 
the  stake  at  a  point  eight  inches  below  the  sighting  mark. 


^ 


EXPERIMENT   TO   SHOW   THE    EARTH  S   CURVATURE. 

^It  is  by  measurements  depending  on  this  principle  tliat  the 
exact  shape  of  the  earth  has  been  ascertained.  A  pendulum  of 
absolute  uniform  length,  weighted  by  a  cannon-ball  weighing 
about  one  hundred  pounds,  is  allowed  to  oscillate  freely.  When 
all  errors  are  corrected  the  rate  of  vibration  will  be  the  same  at 
all  points  of  the  earth's  surface  equally  distant  from  the  centre.  At 
any  part  nearer  the  centre,  as  the  poles,  the  rate  of  vibration  is 
slightly  faster  ;  at  any  place  more  remote  they  will  be  slower.  The 
United  States  Coast  and  Geodetic  Survey  has  carried  on  a  series  of 
pendulum  observations  covering  a  period  of  many  years  witli  the 
results  noted  on  p.  13.  Professor  Ferrel  has  shown  that,  theo- 
retically, the  level  of  the  sea  between  the  20th  and  27th  parallels 
is  about  thirteen  metres  (40  ft.)  higher  than  it  would  be  if  the 
earth  were  a  true  spheroid. 

^  Any  change  in  the  inclination  of  the  earth's  axis  would  have 
the  effect  of  producing  decided  changes  of  climate.  For  instance, 
if  the  inclination  were  increased,  the  limits  of  the  frigid  zones 
would  be  pu.shed  farther  toward  the  equator.  That  is,  if  the  in- 
(dination  of  the  axis  were  forty  degrees  instead  of  twenty-three 
and  one-half,  the  polar  circles  would  each  be  forty  degrees  from 
the  poles,  and  the  tropics  would  be  each  forty  degi-ees  from  the 
equator. 


CHAPTER   II 

THE    STRUCTURE    OF   THE    EARTH 

In  the  long  period  of  time  that  has  ela]ised  since  tlie 
earth  was  glowinu;  Avith  intense  heat,  the  substances  com- 
posing it  seem  to  have  adjusted  theniselves  in  accordance 
with  the  laws  of  gravitation ' — that  is,  the  heaviest  kinds  of 


IDEAL   SECTION     lUROUoH     IHE    EARTH 

The  tbiclini'<:^  of  tl?r  i\in'ons  envelopes  is  greatly  di^torteil. 

matter  are  nearest  the  centre.  Structiiridly  the  earth  con- 
sists of  a  dense  and  practically  solid  globe,  the  litJiosphere, 
nearly  covered  with  a  comparatively  thin  layer  of  water, 

20 


THE  STRUCTURE  OF  THE  EARTH     21 

the  hydrosphere  or  water  envelope,  the  whole  surrouuded 
by  an  envelope  of  gaseous  matter,  the  atmosphere. 

The  shape  of  the  lithosphere  and  the  condition  of  the 
substances  composing  it,  all  go  to  show  that  in  times  past  it 
was  intensely  heated,  and  that  much  of  the  rock  composing 
it  has  been  in  a  molten  condition.  The  globular  form  is 
the  only  one  that  would  naturally  result  from  the  action  of 
gi'avitation  on  a  plastic  or  fluid  body ;  and  the  flattening 
at  the  poles  is  most  reasonably  explained  by  the  supposi- 
tion of  a  rotation  on  its  axis  while  it  was  still  plastic. 

The  density  of  the  lithosphere,  together  with  the  waters, 
is  about  that  of  iron  ore  "^ — that  is,  bulk  for  bulk,  it  is  about 
five  and  one-half  times  as  heavy  as  water.  At  the  surface, 
however,  the  density  of  the  rocks  is  not  much  more  than 
half  as  great;  it  is  certain,  therefore,  that  the  substances 
forming  the  interior  are  much  heavier  than  those  occur- 
ring at  tiie  surface. 

The  Rock  Envelope. — The  outer  part  of  the  litho- 
sphere is  a  shell  of  more  or  less  friable  material  called  the 
rock  envelope,  or,  popularly,  the  "  crust  of  the  earth."  It 
surrounds  an  intensely  heated  interior.^  The  rock  enve- 
lope itself  has  lost  so  much  of  the  heat  it  once  had  that  it 
is  comparatively  cold  ;  the  amount  of  heat  it  radiates  is 
about  equal  to  that  which  it  receives  from  the  sun. 

That  the  interior  of  the  lithosphere  is  very  hot,  however, 
cannot  be  donl)ted ;  for  in  every  place  where  the  rock  en- 
velo{)e  has  been  penetrated  by  deep  borings,  a  constant 
increase  of  temperature  is  observed — the  greater  the  depth 
the  higher  the  temperature.'  The  thickness  of  the  rock  en- 
vehjp(!  is  not  known,  but  at  a  depth  of  less  than  forty  miles 
it  is  thonglit  that  the  temperature  is  high  enough  to  fuse 
the  UKist  njfractor}'  substances.  The  broken  folds  of  the 
outer  surface  have  revealed  something  of  its  character  to 
tlie  depth  of  several  miles.     Borings  have  been  made  to  a 


22  PHYSICAL   GEOGRAPHY 

depth  of  a  little  more  than  a  mile  (Table  II.,  Appendix), 
but  beyond  the  slight  knowledge  obtained  from  these, 
nothing  positive  is  known  about  its  interior. 

The  Water  Envelope. — About  four-fifths  of  the  sur- 
face of  the  rock  envelope  is  covered  by  a  comparatively 
thin  layer  of  water,  the  hydrosphere.  The  water  not  only 
exists  in  a  free  state,  at  the  surface,  but  in  chemical  com- 
bination it  is  a  constituent  of  various  kinds  of  rock  ^  that 
occur  at  or  near  the  surface. 

The  waters  of  the  earth  form  a  most  important  constitu- 
ent so  far  as  life  is  concerned.  Water  is  an  essential  ele- 
ment to  the  existence  of  life  ;  for  not  only  does  it  form  the 
greater  part  of  every  plant  or  animal,  but  it  is  also  the 
chief  vehicle  by  wliicli  nutrition  is  distributed  throughout 
the  various  parts  of  the  body  of  the  animal  or  the  plant. 
Within  a  range  of  a  very  few  degrees  of  temperature,  water 
exists  in  one  or  another  of  three  forms — a  solid,  ice  ;  a 
liquid,  water  ;  and  an  invisible  vapor,  often  called  "steam." 
Water  in  one  or  the  ofclier  of  its  forms  is  the  agent  by 
which,  more  than  any  other,  the  surface  of  the  rock  enve- 
lope has  been  sculptured ;  therefore  it  has  a  ver}'  impor- 
tant part  in  the  science  of  phjsiography. 

The  Atmosphere. — The  atmosphere  consists  of  a  mixt- 
ure of  gaseous  substances — namely:  nitrogen,  oxygen, 
water  vapor,  and  carbon  dioxide.  Of  these  oxygen  is  the 
substance  required  in  the  breathing  of  animals ;  carbon 
dioxide,  the  gas  formed  when  coal  or  carbon  "  biirus,"  is 
essential  in  the  breathing  of  plants ;  nitrogen  forms  a  part 
of  the  body  structure  in  both  animals  and  plants ;  and 
water  vapor  is  the  form  in  Avhicli  the  fresh  water  is  carried 
from  the  sea  to  the  laud.  The  atmosphere,  therefore,  is 
just  as  essential  to  life  as  the  water  envelope. 

The  thickness  of  the  atmospheric  envelope  is  not  known. 
Various  estimates  place  it  between  one  hundred  and  two 


THE  STKUCTURE  OF  THE  EARTH     23 

hundred  miles.  At  the  latter  estimate,  on  a  globe  one  yard 
iu  diameter,  the  depth  of  the  atmosphere  in  proportion 
would  be  about  one-half  an  iuch.'^     Illustrate  by  diagram. 

Keeping  Nature's  Balance. — The  three  envelopes  are 
constantly'  aetiiig  and  reacting  upon  each  other,  and  at  the 
same  time  each  has  certain  movements  of  its  own.  The 
movements  of  the  rock  envelope  have  changed  the  level  of 
its  surface  so  that  the  waters  are  divided  from  the  land,  and 
the  sni-face  of  the  land  has  been  wrinkled,  crumpled,  and 
folded  so  as  to  form  the  plateaus,  ranges,  and  valle3s.  The 
heat  of  the  sun  causes  a  part  of  the  ocean  waters  to  take 
the  form  of  vapor,  and  the  latter,  mingled  with  the  air, 
tlows  over  the  land.  Being  chilled,  the  vapor  again  takes 
the  form  of  rain,  or  of  snow,  and  falling  on  the  land  wears 
away  its  surface.  The  water  gathers  into  channels  and, 
carrying  the  mingled  particles  of  rock  waste  in  its  flood, 
flows  back  to  the  sea  and  there  deposits  them. 

And  so  the  cj'cle  of  change  ever  goes  on.  At  the  plane 
where  th(3  atmosphere  rests  upon  the  land  and  the  sea  the 
physiographic  processes  that  modify  the  earth's  smface  are 
ever  in  action. 

Vertical  Movements  of  the  Rock  Envelope. — The 
changes  in  the  smiace  of  the  rock  envelope  that  are  most 
noticeable  are  the  weaiing  awa}'  of  the  land  and  the  trans- 
])()rtati()ii  of  the  lock  Avaste  to  lower  levels.  That  is, 
water  falling  as  rain  loosens  particles  of  rock,  while 
streams  cany  it  seaward.  If  the  land  were  evei-ywherc 
level,  the  i-uii-ol't' of  water  could  wear  away  but  little  of  it; 
but  vertical  movements  of  the  surface  that  arc^  apparent 
onlv  after  long  intervals  of  time  are  taking  place,  and 
these,  making  new  slopes,  have  giv(!n  the  I'un-ofl'  waters 
inci-eased  weM)"ing  pow«!r. 

M(jvem<'nts  of  the  rock  envelope  in  limes  ])ast  have  di- 
versified  its  siii'fac(3  with   liiglilaiids  and    lowlands,  nioun- 


24  PHYSICAL   GEOGKAPHY 

taius  and  valleys,  and  similar  movements  are  going  on  at 
the  present  time.  Probably  no  part  of  the  earth  is  free 
from  them,  but  they  are  most  clearly  observed  along  sea- 
shores.    Thus,  the  coast  of  New  Jerse}^  is  sinking ;"  and 


AN    UPLIFTED   COAST,   SAN   PEDRO,   CAL. 

From  a  survry  made  by  Mcn'ck    Reynolds,  Jr.       The   successively  formed  beaches  are  shown 

by  the  strata  of  shells  and  sand. 

SO  also  is  much  of  the  coast  around  the  Gulf  of  Mexico,  the 
Zuyder  Zee,  and  the  delta  of  the  Ganges-Brahmaputra. 
The  coast  of  the  New  England  Plateau  has  subsided  until 
the  sea  has  flooded  the  coast  plain  and  the  lower  valleys, 
and  has  buried  most  of  the  old  river  mouths.  The  multi- 
tude of  bays  and  fjords  that  characterize  this  coast  are 
examples  of  "  drowned "  valleys.  On  the  other  hand, 
parts  of  the  Mediterranean  basin,  of  the  California  coast,^ 
the  Scandinavian  peninsula,  and  the  basin  of  Great  Salt 
Lake  are  rising. 

In  nearly  every  instance  in  areas  to  which  extensive 
sediments  are  being  carried  there  is  evidence  of  sinking  ; 
while,  as  a  rule,  areas  that  are  being  denuded  are  rising. 
It  is  evident,  therefore,  that  vertical  movements  of  the 
lock  envelope — that  is,  uplift  and  subsidence — are  defin- 
i'ely  connected  with  the  wasting  of  the  land  and  the  trans- 
fer of  sediment. 

The  cause  or  causes  of  these  earth  movements  are  not 
known,  but  it  is  believed  that  the  gradual  contraction  of 
the  rock  envelope  to  fit  itself  around  a  move  rapidly  shrink- 


THE   STRUCTURE   OF   THE   EARTH 


25 


ing  interior  is  the  chief  cause.  There  is  evidence,  too,  that 
gravitation  is  a  factor.  The  removal  of  great  amounts  of 
rock  waste — often  many  cubic  miles  in  volume — from  one 
locality  to  another,  relieves  weight  at  one  place  and  in- 
creases it  at  the  other.**  Therefore  it  is  inferred  that  a 
sinking,  because  of  the  increased  load,  occurs  at  the  latter 
place,  and  an  uplift  at  the  former,  on  account  of  the  less- 
ened weight. 

The  eli'ects  of  these  earth  movements  are  very  far-reach- 
ing. The  gi'eat  highland  regions  of  the  earth,  with  their 
ridges  and  folds,  are  probably  direct  results,  and  it  is  not 
improbable  that  the  uplift  of  the  continents  themselves 
was  also  due  to  them. 


-' 

^^^^K 

^._ 

■i 

_.— «! 

^^^K  ; 

1 

::m 

■■ 

m 

:,.„«^-Ji«l 

n^H 

ftMub^^lOrapH^^  ^^s^'lflSBH^B 

^^ 

IGNEOUS   ROCK  :    A    FLOW   OF   LAVA 


Rock  and  Its  Formation.— To  almost  every  mineral 

suljstaiico  tliat  fonns  a  ])art  of  the  earth,  the  term  rock  is 
ap])li<'d.  'i'hus,  clay,  s;uid,  gravel,  limestone,  (piartz,  gran- 
ite, lava,  and  even  the  fine,   wind  blown   rock   waste,  are 


26  PHYSICAL   GEOGRAPHY 

each  called  rock  ;  and  so  also  is  a  conibiuation  or  any  mixt- 
ure of  tlieui.  In  many  instances  there  is  no  doubt  at  all 
how  the  rock  has  been  formed,  or  whether  it  has  been  al- 
tered or  not,  because  the  whole  process  of  its  formation 
has  been  carried  on  in  ])lain  sight.  Thus,  when  a  volcano 
or  a  fissure  pours  out  a  flood  of  molten  lava  there  is  no 
question  about  how  the  rock  got  into  place,  or  whence  it 
came.  The  lava,  when  it  has  hardened,  may  be  glassj',  or 
metallic  in  appearance,  or  it  may  be  like  cinder  or  furnace 
slag  ;  but  there  are  always  qualities  about  it  that  deter- 
mine its  origin. 

Beyond  a  depth  of  a  few  thousand  feet  from  the  surface, 
nothing  positive  is  known  about  tlie  substances  of  which 
the  rock  envelope  is  composed.  It  is  certain,  however, 
that  most  of  the  rock  now  at  the  surface  consists  of  sedi- 
ments carried  into  place  by  running  water  and  deposited 
in  the  form  of  layers  or  strain  that  afterward  hardened  into 
compact  rock.  But  these  sediments  must  have  come  from 
somewhere,  and  there  is  but  one  place  from  which  they 
could  be  derived — namely,  from  the  rock  envelope  itself. 

Now,  no  one  knows  what  the  primitive  or  first  rock  that 
formed  the  crust  of  the  earth  may  have  been,  but  certain 
kinds  of  rock  have  been  found  underlying  the  water-formed 
sediments  from  which  the  latter  seem  to  be  derived.  Or- 
dinary granite  is  an  example  of  this  kind  of  rock,  and 
granitic  rocks  are  very  abundant.  There  are  various 
kinds  of  granite,  but  the  most  common  varieties  contain 
minerals  of  which  nearly  all  the  elementary  rocks  them- 
selves are  composed. 

One  of  these  minerals  is  silica,  of  which  quartz  and  sea 
sand  are  the  best  examples.  Another  is  felspar,  a  mineral 
which,  decomposed,  yields  clay,  potash,  lime,  and  soda. 
Another  mineral  is  hornblende,  which  decomposes  mainly 
into  iron,  lime,  and  silica.    Still  another  constituent  usually 


THE  STRUCTURE  OF  THE  EARTH     27 

present  is  mica,  popularly  called  "  isinglass ;  "  like  felspar 
it  also  decomposes  into  clay,  silica,  lime,  and  a  num.ber  of 
other  substances. 

EXERCISE.— Procure  one  or  more  specimens  of  granite,'"  and  with 
th"?  aid  of  a  magnifying-glass  observe  the  following  directions.  Look 
for  small  clusters  of  foliated  or  "  leafy  "  mineral  ;  it  may  be  whitish 
or,  perhaps,  green  or  brown  ;  this  mineral  is  mica.  If  no  mica  is 
found,  look  for  jet  black  crystals  or  masses  ;  this  is  hornblende  ;  it  is 
usually  opaque,  but  sometimes  translucent.  Find  the  white,  trans- 
lucent mineral  with  glassy  lustre  ;  it  is  quartz,  or  silica,  and  it  is  apt 
to  form  the  chief  bulk  of  the  rock.  Look  also  for  an  opaque  mineral 
varying  from  yellowish-white  to  pink  in  color ;  possibly  it  will  break 
into  fragments  having  flat  sides,  or  cleavage  planes ;  this  mineral  is 
felspar  ;  it  has  different  crystalline  forms  accordingly  as  it  contains 
lime,  potash,  or  soda. 

Igneous  Rocks. — There  are  certain  surface  rocks  that 
have  cooled  from  a  molten  condition,  and  of  these  the 
lavas  of  volcanoes,  though  not  the  most  abundant,  are  per- 
haps the  best  known.  The  Hawaiian  Islands  are  mainly 
great  piles  or  domes  of  lava,  and  this  kind  of  rock  is  com- 
mon in  most  mountainous  regions.  In  many  instances  the 
molten  rock  has  been  ejected  from  long  fissures  and  has 
cooled  slowly  ;  in  this  form  it  is  usually  known  as  basalt, 
or,  if  it  breaks  into  regular  blocks,  trap.  The  Palisades  of 
the  Hudson,  Fiugal's  Cave,  and  the  Giant's  Causewa}'  are 
examples. 

All  the  foregoing  are  commonly  called  vulcanic  or  ifpie- 
ous  rocks  ;  consult  a  good  dictionary  and  learn  why  these 
names  are  applied.  Igneous  rocks  are  usuall}^  found  in 
mountainous  regions,  or  in  localities  from  which  the  sedi- 
mentary rock  has  been  removed.  Granite  rocks  prevail  in 
th(!  New  England  Plateau;  igneous  rocks  are  abundant  in 
thii  Western  Highlands. 

Sedimentary  Rocks. — Altiiough  the  sedimentary  rocks 
that  prevail  in  such  a  great  extent  of  the  laud  are  derived 


28  PHYSICAL   GEOGRAPHY 

from  the  granitic  and  other  vnlcanic  rocks,  there  is  nothing 
about  them  to  indicate  their  ch)se  relation  to  the  lattei-. 
The  making  of  tirm  rock  out  of  kjose  sediments  is  a  some- 
what complex  process.  Let  us  follow  the  formation  of 
sandstone.  In  the  first  place  the  grains  of  quartz  are 
rounded,  and  in  the  second  place  thej  are  uniform  in  size. 
The  rock  from  which  they  came,  probably  granite,  has 
crumbled,  and  water  has  sorted  the  various  minerals  from 
one  another.  Tlie  waves,  beatiug  the  fragments  of  quartz 
and  rubbing  them  against  one  another,  liave  not  only 
rounded  the  grains,  but  they  have  also  sorted  them  ac- 
cording to  size,  and  piled  them  in  a  nearly  flat  layer. 
True  sand,  therefore,  is  nearly  always  a  formation  of  beaches 
or  of  water  in  motion. 

In  time  the  beach  is  lifted  up  above  seadevel  and  cov- 
ered deep  with  vegetable  remains  mixed  wdth  loam.  Water, 
in  one  form  or  another,  flows  over  or  stands  upon  the 
surface ;  and  if  the  water  contains  lime  in  solution  it  will 
leach  through  the  layer  of  sand  and  cement  the  gi-ains, 
forming  sandstone. 

In  most  instances,  clay  banks  are  derived  from  granitic 
and  similar  rocks.  Felspar  decomposes  into  clay,  and  the 
latter,  being  very  light  and  fine,  is  carried  ofl"  by  the  water, 
settling  b}^  itself,  while  the  heavier  materials  remain.  In 
many  instances  the  clay  is  spread  over  large  areas.  Pos- 
sibly it  remains  in  the  stiff,  pasty  form  by  which  it  is 
commonly  kuowai  ;  more  likely  pressure,  heat,  and  moisture, 
acting  together,  convert  it  into  slate. 

It  is  not  diflicult  to  understand  how  rivers  and  other 
running  waters  are  active  workers  in  making  rock,  because 
one  can  almost  always  find  clay-banks,  gravel-beds,  and  other 
sediments  that  have  been  brought  down  stream  and  dis- 
tributed by  the  water."  It  is  not  so  easy  to  understand 
how  rocks  are  found  at  the  bottom  of  the  sea ;  as  a  matter 


THE  STKUCTURE  OF  THE  EARTH      29 


SEDIMENTARY   ROCK,   NEAR   OLEAN,  N.  Y. 
The  face  of  the  cliff  is  one  side  of  a  channel  of  the  river. 

of  fact,  however,  piMjbably  more  sedimentary  rock  has  been 
formed  in  ocean  and  lake  beds  than  in  any  other  pUices. 
In  very  many  instances  these  rocks  are  largely  composed 
of  the  remains  of  animals  so  small  that  several  thousand  of 
them  together  would  not  be  so  large  as  the  head  of  a  pin. 

The  sea,  especially  in  regions  of  warm  water,  contnius 
many  thousand  species  of  such  animals ;  moreover  tbry 
multiply  with  great  rapidity.  But  the  animals  are  short- 
lived, and  as  soon  as  tlic}^  die  their  bodies  sink  to  iho 
bottom.  The  mineral  remains  of  these  organisms  consist 
mainly  (^f  lime  or  silica,  and  in  time  tlie  thick  layer  that 
accumulat(?s  finally  becomes  C(;ment(;d  into  rock.  The 
growth  of  rock  in  this  way  is  slow,  it  is  true,  but  time  alone 


30  PHYSICAL   GEOGRAPHY 

is  reqiiiitui  to  in:iko  such  layers  of  very  great  thickness. 
The  chalk  cliU's  of  England  and  France  were  formed  in  this 
manner,  and  they  aggregate  nearly  half  a  mile  in  thickness. 
The  limestones  of  tlie  Mississippi  Y'alley  also  accmnulated 
on  sea-bottoms  and  have  about  the  same  thickness. 

Metamorphic  Rocks, — There  are  many  instances  in 
which  the  character  of  sedimentary  rocks  has  been  sub- 
sequently changed.  Thus,  by  pressure  and  heat  in  the 
presence  of  moisture,  beds  of  clay  have  been  transformed 
into  layers  of  gritty  slate ;  chalk  and  limestone  have  be- 
come crystalline  marble  ;  and  bituminous  coal  has  become 
anthracite.  Certain  kinds  of  granitic  rock,  especially 
gneiss  or  "  stratified  granite,"  are  metamorphic.  Older 
granitic  rock  has  crumbled,  and  the  rock  waste  has  been 
cemented  into  firm  rock  again  with  but  little  alteration. 

One  might  infer,  therefore,  that  the  older  and  deeper 
stratified  rocks  would  be  thus  changed.'^  This  is  usually 
the  case.  The  weight  of  the  overlying  rock  produces  im- 
mense pressure,  and  the  changes  resulting  from  the  moist- 
ure within  them  greatly  alter  their  appearance.  Many  of 
the  older  rocks,  indeed,  are  much  like  igneous  rock  in  ap- 
pearance. Rocks  that  form  a  part  of  mountain  folds  are 
apt  to  be  metamorphic  on  account  of  the  pressure  that 
results  from  the  folding  and  crumpling. 

EXERCISE.— Procure  specimens  of  clay  and  slate,  chalk  (not  crayon) 
and  marble,  bituminous  (soft)  coal  and  anthracite.  Examine  each  pair 
with  reference  to  hardness,  foliation,  crystalline  appearance,  and  den- 
sity (weight  of  pieces  of  equal  size).  Make  a  list  of  the  rocks  occurring 
in  the  neighborhood  in  v/hich  you  live,  and  classify  them  as  igneous, 
sedimentary,  or  metamorphic. 

Order  of  the  Strata. — Most  of  the  sedimentary  rocks 
were  deposited  in  horizontal  layers,  but,  on  account  of  the 
vertical  movements  of  the  rock  envelope,  they  are  often 


THE   STRUCTURE   OF   THE.  EARTH 


31 


fonud  ill  oblique  positions.  Sometimes  they  occur  in  gen- 
tle folds ;  l)ut  in  mountainous  regions  they  are  much 
crumpled  and  broken.  In  some  of  the  old  sea-beds  now 
raised  above  the  surface  the  strata  are  undisturbed. 


SEDIMENTARY   ROCK;    SECTION   THROUGH   THE   CANON   OF   THE   COLO- 
RADO   RIVER 

The  level  of  the  strata  Ijas  >ioi  been  dibliiihed. 

It  is  by  studying  the  upturned  edges  of  broken  and  tilt- 
ed strata  that  the  story  of  the  earth  has  been  read.  Each 
stratum  is  a  chapter  by  itself,  and  to  read  the  history  prop- 
erly it  is  best  to  begin  with  the  lowest.  It  is  not  always 
easy  to  tell  the  relative  position  of  strata  at  some  distance 
from  one  another,  but  as  each  stratum  has  fossils,  or  ani- 
mal remains  peculiar  to  itself,  the  position  is  usually  de- 
termined by  the  kind  and  character  of  these. 


S1:D1.MENTARY    rock  :    Tll.TED   STRATA 

The  total  thickness  of  the  stratified  rocks  is  estimated 
at  upward  of  twenty  miles.  There  is  no  locality  known, 
and  noue  exists,  in  which  all  the  various  strata  are  found — 
no  locality  is  known  in  which  even  any  considerable  num- 
l)rr  occur.  Not  infrequently  very  old  rocks  ai'e  overlaid 
Itv  those,  of  tli(!  most  recent  formations  ;  all  the  intermedi- 
ate strata  an;  missing.''' 

To  tti«!  lowest  strata,  that  do  not  ditTler  mucli  fiom  the 
granitic  rocks  and  possilily  inchide  some  of  tiiem,  tlie  name 


32 


PHYSICAL   GEOGRAPHY 


Arcluean^^  is  given.     They  seem  to  be  tlie  foundation  of 
the  continents  and  the  floor  of   the  oceans.     The  decay 

and  wearing  away  of  these  has 
formed  the  material  of  Avhich 
nearly  all  the  sedimentary  rock 
is  composed.  "  The  waste  of  the 
old  land  is  the  material  of  the 
new.'' 

The  remaining  strata  are 
named  in  accordance  with  the 
character  of  the  life  forms  that 
existed  when  the  rocks  that 
compose  them  Avere  undergoing 
formation.  Upon  the  Archaean, 
rest  the  rocks  of  the  Palceozoic 
era — the  age  of  the  earliest  life 
forms.  Then  follow  the  rocks 
of  the  Alesozoic,  or  middle-life 
era;  the  Cenozoic,  or  era  of  re- 
cent life ;  and,  last  of  all,  the 
era  of  man. 

Archaean  Era. — In  Archaean  times  North  America  con- 
sisted mainly  of  a  narrow,  V-shaped  strip  of  land  south  of 
Hudson  Bay.  The  crests  of  the  Appalachian  Mountains 
were  jnst  above  the  sea  level  ;  the  Black  Hills  and  one  or 
two  peaks  of  the  Bocky  Mountains  had  also  just  emerged. 
The  general  form  of  the  American  continent  was  outlined 
in  Archaean  times.  With  the  possible  exception  of  a  few 
species  resembling  the  sponge,  no  forms  of  life  are  found 
in  Archaean  rocks.      {See  illustration,  p.  34.) 

Palaeozoic  Era. — -The  Palaeozoic  era  was  of  very  long 
duration.  The  sediments  composing  it  are  25,000  feet 
thick  in  places.  The  greater  part  of  Europe  and  North 
America  were   above   sea- level  during  this  period,  but  the 


UNCONFORMABLE  STRATA: 
CANON  OF  THE  COLORADO  RIVER 

The  tilted  strata,  originally  horizontal, 
were  deposited  on  the  surface  of  the 
igneous  rock:  Subsequently  the  upper 
layers  were  deposited  on  the  broken 
surface  of  the  tilted  layers. 


THE   STRUCTURE   OF   THE   EARTH 


33 


land  was  mauy  times 
uplieaveJ  and  sub- 
merged. In  North 
America  the  greater 
part  of  the  INIississip- 
pi  Valley  was  a  shal- 
low iuland  sea,  that 
later  became  an  im- 
mense marsh. 

In  the  variety  and 
extent  of  life  forms 
the  Palaeozoic  era  is 
the  most  noteworthy 
of  all  the  geological 
periods.  It  began 
with  the  lowest  form 
of  spcmges  and  closed 
with  the  advent  of 
mammoth  reptiles. 
During  this  period  an- 
imals with  backbones 
appeared  for  the  first 
time.  Insects  Avere 
numerous,  and  toward 
the  close  reptiles  ex- 
isted. Fishes  and 
mollusksseem  to  have 
been  the  prevailing 
forms. 

'V\w  climate  wms 
warm  and  moist.  Tln' 
vast  accumulations  of 
vegetal )ln  )natt(tr  tliat 
are  now  the  coal  fields 


ORDER   OF   STRATA 


34 


PHYSICAL   GEOGRAPHY 


were  found  in  swamps  of  this  age.''^'  In  North  America 
these  swamps  covered  much  of  the  area  that  is  now  the 
central  United  States. 

Mesozoic  Era, — During  the  Mesozoic  era  both  North 
America  and  Europe  had  grown  to  about  their  present 
shape.  In  the  former  division  the  Gulf  of  Mexico  reached 
as  far  north  as   the  mouth  of  the    Ohio,   and    a  n(jrth- 

western  branch  of  it  ex- 
tended nearly  to  the  50th 
parallel.  In  Europe  all 
tlie  principal  mountain 
ranges '"  and  the  higher 
elevations  of  land  most 
probably  had  been  raised 
permanently  above  sea- 
level. 

It  was  an  age  of  gigan- 
tic reptiles.  The  animals 
of  some  species  were  from 
sixty  to  eighty  feet  in 
length.  For  the  first  time 
birds  appeared.  They 
were  very  much  like  rep- 
tiles, however,  and  in 
some  species  they  had,  instead  of  horn}'  beaks,  heavy  jaws 
with  socket  teeth. 

Cenozoic  Era. — This  era  was  largely  one  of  uplift  and 
mountain-making,  although  both  in  North  America  and 
Europe  the  various  ranges  and  systems  had  received  defi- 
nite forms.  The  former  was  a  continent  of  vast  fresh-water 
lakes  ;  the  latter  of  inland  seas. 

Most  of  the  life  forms  that  fiourished  in  preceding  ages 
were  common,  but  one  great  step  in  advance  maybe  noted 
— the  appearance    of   mammals.     Their   genera  included 


NORTH   AMERICA   IN   ARCH^AN   TIMES 

The  shaded  area  shows   the  part   of  the   eonlineitt 
above  sea-te'vel. 


THE   STRUCTURE   OF   THE   EARTH 


35 


the   elephant,  camel,''  rhiuoceros,  wolf,  deer,   and  horse.^^ 
There  was  a  cousideralile   advance  in  plant-life,  and  the 
forest  trees  both  of  North 
America  and  Europe  in- 
cluded most  of   the   spe- 
cies fonnd  to-daj. 

Quaternary  Age.  — 
The  abrupt  close  of  the 
Ceuozoic  era  was  prob- 
ably due  to  an  elevation 
of  a  large  part  of  North 
America  and  Europe  from 
1,000  to  2,000  feet,  and  a 
ilecided  lowering  of  tem- 
perature. The  ice  and 
snow  of  the  north  polar 
regions  crept  southward 
until  it  enveloped  nearly     north  America  in  cenozoic  times 

all     of      Europe      and     the    TUc  umliiiiiccl  arej  shows  the  part  o/ tin- Lon/niait 
1  above  sea-level. 

greater  part  of  the  United 

States.  This  accession  of  ice  is  commonly  known  as  the 
(jlacial  epoch.  It  is  marked  on  a  stupc^jdous  scale  by  a 
jiiovement  of  drift  similar  to  that  which  marks  the  gla- 
ciers of  the  present  time. 

The  changes  of  the  Quaternary  age  were  disastrous  to 
life.  In  the  area  covered  by  glacial  ice  most  of  the  spe- 
cies of  larger  mammals  perished.  The  cave  bear,  horse, 
A\olf,  and  reindeer  survived.  Many  species  of  plants  were 
destroyed,  but  many  escaped. 

That  man  existed  before  the  close  of  the  glacial  epoch 
seems  certain.  In  the  caverns  of  Belgium,  Germany,  and 
Italy  the  b(jncs  of  man  have  Ijeen  found  in  caves  along 
with  the  skeletons  oi  animals  and  various  implements  of 
the  chase.     From   tlie   few  scraps  of   unwritten  history  it 


36 


PHYSICAL  GEOGRAPHY 


seems  that  primitive  man  was  a  savage  of  the  lowest  type. 
He  lived  in  caves  and  obtained  his  food  by  hunting  and 
fishing.    He  did  not  cultivate  the  soil  nor  did  he  have  any 


THE    UNITED  STATES   AT   THE   BEGINNING   OF  THE   QUATERNARY   AGE 

The  shaded  area  shou'S  the  part  added  in  recent  times. 

domestic  animals.  He  had  learned  the  use  of  fire,  how- 
ever, and  from  that  moment  his  intellectual  development 
was  a  question  of  time  only. 

QUESTIONS  AND  EXERCISES— A  mixture  of  iron  filings,  sand, 
and  meal  is  gently  shaken  in  a  glass  :  what  position  will  the  compo- 
nents take  when  they  come  to  rest  ?    Explain  why. 

It  is  sometimes  assumed  that  the  rock  envelope  is  about  forty  miles, 
and  the  atmosphere  about  two  hundred  miles,  in  thickness.  Construct 
a  diagram  on  the  blackboard  or  on  paper,  showing  the  relative  thick- 
ness of  each  on  scale  in  the  ratio  of  4000  :  40  :  200. 

Obtain  specimens  of  iron  ore,  marble,  and  dry  clay,  and  compare 
the  weight  of  pieces  of  the  same  size.  If  possible  find  the  specific 
gravity  of  each.  Determine,  or  judge  by  *'  hefting,"  the  relative  weight 
of  the  various  kinds  of  rock  in  the  neighborhood  in  which  you  live. 

Note  and  describe  any  instances  within  your  personal  knowledge  of 
the  action  of  water  on  the  rock  envelope  ;  explain  the  nature  of  the 
changes  and  how  they  have  been  brought  about. 

Study  the  various  rock  formations  in  the  neighborhood  in  which  you 
live  and  classify  them  according  to  their  origin— that  is,  as  sediment- 
ary or  igneous. 

Make  a  collection  of  them  for  future  use. 


THE  STRUCTURE  OF  THE  EARTH     37 

A  stream  flows  over  a  bed  of  limestone  rock  that  is  slightly  soluble, 
into  a  lake  without  an  outlet ;  what  changes  in  the  formation  of 
rock  are  likely  to  occur  ?  Will  the  rock  formed  be  stratified  or  un- 
stratified  ?     In  what  way  may  it  become  fossiliferous  ? 

From  the  official  State  reports  find  the  order  and  distribution  of  rock 
strata  in  the  State  in  which  you  live,  and  from  the  information  given 
construct  a  geological  map. 


COLLATEEAL   READING 

Powell.— Physiography  of  the  United  States,  pp.  22-29. 
Le  Coxte. — Elements  of  Geology,  pp.  127-1B2. 
Mill.— Realm  of  Nature,  pp.  211-230,  249-261. 
SHA.LER. — First  Book  of  Geology,  pp.  107-124. 


NOTES 

'That  is,  the  substances  specifically  heaviest  are  nearest,  and 
the  lightest  are  farthest,  from  the  centre. 

^  Iron  and  its  compounds  form  one  of  the  most  abundant  con- 
stituents of  the  earth,  and  it  is  likewise  one  of  the  most  abundant 
substances  of  the  sun  and  of  some  of  the  fixed  stai's.  All  the  me- 
teorites that  have  landed  on  the  earth  contain  it,  and  in  most  of 
them  it  is  the  chief  element  present. 

^  It  must  not  be  inferred  from  this,  however,  that  the  heated  in- 
terior is  in  a  liquid  condition  ;  on  the  contrary,  the  earth  be- 
haves like  a  solid  but  somewhat  elastic  body.  The  melting  or 
fusing  of  a  substance  depends  not  on  temperature  alone,  but  on 
pressure  as  well.  With  increase  of  pressure,  the  temperature  of 
fusion  is  also  raised  ;  and  the  great  weight  of  the  overlying  rock 
may  possibly  produce  a  pressure  great  enough  to  pi'event  lique- 
faction. 

*  The  increase  varies  not  only  in  different  localities,  but  in  dif- 
ferent kinds  of  rock,  the  average  being  one  degree  for  each  sixty 
or  seventy  feet.  In  a  certain  boring  in  Upper  Silesia,  6,700  feet 
deep,  there  is  a  slight  decrease  in  the  ratio,  but  a  marked  in- 
crease in  the  actual  temperature  at  the  greater  depths. 

^  The  crystalline  form  of  many  I'oeks  is  due  to  the  water  they 
contain  in  chemical  combination,  and  tliere  are  but  few  rocks  of 

4  5  6  ;^  4 


38  PHYSICAL   GEOGEAPHY 

wliich  water  does  not  form  a,  considerable  part.  It  is  by  no  means 
impossible  that  the  watei-s  of  the  earth,  in  time,  maj^  be  aljsorbed 
in  this  way,  disappearing  as  free  water,  to  reappear  in  chemical 
combination. 

*  About  one-fifth  of  the  atmosphere  consists  of  fi-ee  oxygen,  an 
element  that  forms  also  a.bout  one-half  the  weight  of  the  earth's 
crust,  so  far  as  can  he  estimated.  In  time,  po.ssiVjly,  all  the  free 
oxygen  will  be  absorbed,  entering  into  chemical  combination  with 
other  substances. 

'  In  most  instances  the  rate  of  sinking  is  about  equal  to  the 
depth  of  the  layer  of  sediment  annually  spread  over  the  surface. 
The  amount  of  sediment  carried  into  the  Gulf  of  Mexico  is  enor- 
mous, but  it  does  not  apparently  raise  the  level  to  any  great  ex- 
tent ;  few  parts  of  the  made-land  surrounding  the  gulf  are  more 
than  ten  or  fifteen  feet  above  sea-level. 

"*  At  San  Pedro.  California,  the  upward  movement  has  Ijeen  un- 
usually rapid.  Several  layers  of  shells  mixed  with  sand  are  found 
one  above  another,  at  heights  vaiying  from  five  to  fifteen  feet  or 
more.  The  shells  belong  to  species  some  of  which  are  not  now 
extinct,  and  most  of  them  have  been  preserved  in  their  natural 
state.  The  highest  beach  is  nearly  three  hundred  feet  above  sea- 
level.  The  various  beaches  are  so  slightly  weathered  that  they 
seem  scarcely  altered,     ff^ee  illustration,  p.  24.) 

"  According  to  this  principle  the  rock  envelope  of  the  earth 
always  maintains  a  state  t>f  balance,  adjusting  itself  to  the  load 
it  carries.  It  is  readily  illustrated  by  putting  an  ounce  weight 
on  an  inflated  toy  balloon.  The  surface  of  the  balloon  is  de- 
pressed by  the  weight,  but  if  the  latter  be  removed  the  surface 
again  rises  ;  or  if  the  weight  be  moved  from  one  part  of  the  bal- 
loon to  another  the  surface  at  the  one  part  rises  while  at  the  other 
it  sinks. 

■°  Normally,  granite  is  a  mixture  of  mica,  felspar,  and  quartz. 
If  it  contains  hornljlende  instead  of  mica  it  is  called  syenite;  if 
both  mica  and  hornblende  are  present  it  is  syeidtic  granite.  If 
the  felspar  contains  soda  the  granite  is  diorite.  If  the  rock 
shows  layers  it  is  then  called  gneiss. 

"  An  interesting  example  of  rock-formation  occurs  at  Sweyney 
Cliffs,  Shropshire,  England.  A  small  stream  of  water  pours  over 
a  red  sandstone  cliff,  mainly  in  the  form  of  a  rapid.  The  water 
contains  a  considerable  proportion  of  lime  and  magnesia  ;  and  a 


THE   STIIUCTURE   OF   THE   EARTH  39 

species  of  coarse  moss  grows  freely  in  the  saturated  earth  about 
the  stream-bed.  Tlie  mineral  salts  of  the  Avater  are  deposited  co- 
piously on  the  moss,  and  little  ))y  little  the  latter,  together  with 
the  other  matter  entangled,  has  become  so  completely  incrusted 
that  it  forms  a  dyke  about  twenty  feet  wide.  The  dyke  stands 
out,  having  built  itself  from  the  edge  of  thecliS  a  distance  of  ten 
feet  or  more.    About  three  cubic  yards  are  added  each  year. 

'-■  Substances  ordinarily  insoluble  in  water  are  quickly  changed 
when  subjected  to  water  luider  a  liigh  temi)erature.  If  a  thick 
steel  tube,  tilled  with  water  and  fragments  of  granite,  be  intensely 
heated  for  several  hours,  the  larger  part  of  the  rock  will  be  dis- 
solved. Hot  alkaline  water  will  also  dissolve  granitic  rocks,  the 
dissolved  matter  being  precipitated  wlien  the  water  cools. 

"  Thus,  the  rocks  of  the  Mississippi  basin  belong  to  a  very  old 
and  remote  geological  period.  They  are  overlaid  by  a  thin  cover 
of  rock  waste  that  l)el()ngs  cliieHy  to  tlie  most  recent  period. 

'^Tlie  word  Archaaii  means  "the  beginning";  Falaozoic  is 
derived  from  two  Greek  words  meaning  "  early  life  "  ;  3Iesozoic, 
similarly,  is  "middle  life";  and  Cetiozoic,  "recent  life."  The 
Silurian  age  was  named  from  "Silures. "  a  former  name  for  the 
people  of  Wales;  DeDoiiian  comes  from  "Devon,"  England; 
Huroniau,  from  "Huron";  and  Laurentian  from  "St.  Law- 
rence." All  these  names  are  derived  from  the  localities  in  which 
the  rocks  were  first  studied. 

'°  Coal  measures  are  not  confined  to  the  Carboniferous  age  ;  they 
occur  in  all  geological  ages.  Thus,  the  coal  fields  of  the  Pacific 
coast  belong  to  the  Tertiary  age.  Those  of  the  Carboniferous 
age,  however,  are  so  vast  in  extent  tluit  they  overshadow  all 
other  features. 

'*The  uplift  of  the  Pyrenees  Mountains  did  not  occur  until 
nearly  the  end  of  Mesozoic  times. 

"  There  were  several  species  of  cainel  (liiriiig  these  times.  It 
is  interesting  tt>  note  that  this  animal,  now  contined  to  the  east- 
ern continent,  was  a  native  of  the  west. 

'"  The  earliest  sjjecies  of  horse  had,  instead  of  one,  five  toes.  In 
subsequent  times  two  of  these  gradually  disappeared,  'i'he  horse 
of  modern  geological  times  has  but  one  toe,  but  the  "  splint 
bones"  just  above  the  hoof  are  the  toes  of  the  Quaternary  horse. 


CHAPTER  III 


LAND   AND   WATER,   AND   THEIR   OUTLINES 


The  surface  of  tlie  rock  envelope  is  not  smooth,  nor  is 
any  considerable  part  of  it  perfectly  level,  as  the  word  is 
commonly  used.  More  than  three-fourths  of  its  surface  is 
covered  by  the  sea,  but  the  remaining  part  consists  of  very 
irregular  areas  that  are 
higher  than  the  level  of 
the  water.  The  great 
bod}"  of  water  that  covers 
so  much  of  the  rock  en- 
velope is  the  sea  ;  ^  the 
areas  above  sea-level 
constitute  the  land.  The 
lowest  part  of  the  rock 
envelope  below  sea-level 
— that  is,  the  lowest  part 
of    the    sea- bottom — is 

about  five  and  one-half  miles,  and  the  highest  point  above 
it  is  just  about  the  same  distance.  The  average  elevation 
of  the  land  is  not  far  from  '2,000  feet,  but  the  average 
depth  of  the  sea  is  about  2,000  fathoms. 

The  land  aggregates  about  53,000,000  square  miles.  It 
clusters  around  the  north  pole,  and  from  this  circumpolar 
region  it  radiates  toward  Cape  Horn,  toward  the  Cape 
of  Good  Hope,  and  toward  Tasmania.  In  which  hemi- 
sphere is  the  greater  part  V     AVhich  of  the  two  temperate 

41 


OCEANIC               AREA 

C  ONTI  N  E  NTAL 
AREA 

n 

1  3   L    AN  DS 

RhLATlVt    AREAS   OH    LAND    AND    WATER 


42 


PHYSICAL   GEOGRAPHY 


zones  iucludes  the  greater  area  ?  How  many  great  land 
masses,  each  surrounded  by  water,  are  there  ?  The  two 
largest  masses  are  divided  nearly  in  twain,  each  at  the 
central  part,*^  and  the  smallest  is  separated  by  an  arm  of 
the  sea  which  seems  to  have  severed  it  from  the  largest. 
The  three  largest  laud  masses  are  called  vontinents  ;  ^  the 
smaller  ones  islands.  The  line  along  which  the  land  and 
the  sea  meet  is  the  shore  ;  the  narrow  strij)  of  land  next 
the  shore,  the  coast. 

The  Continents, — The  continents  are  so  called  on  ac- 
count of  certain  features  of  their  structure.  Each  one,  for 
convenience,  is  divided  into  grand  divisions,  and  the  latter 


4 

a       1 

Z 

SOUTH 

NORTH 

0       1 

4 

AMER  lC*v 

AMERICA 

AF  RICA 

a    El 

U 

R 

A 

S 

A 

U 

3         \ 

o 
0 

Ui          1 

RELATIVE   AREAS    OF   THE   CONTINENTS   AND   GRAND   DIVISIONS 

are  also  convenient!}^  called  continents.  In  general,  the 
continents  have  a  high  b(jrder  on  one  side  and  a  lower  one 
on  the  opposite  side.  They  are  variously  named,  but  they 
are  usually  styled  the  Eastern,  or  Asian  ;  the  Western,  or 
American  ;  and  the  Australian.  The  shore  of  a  great 
bbdy  of  land  in  the  south  circumpolar  regions  is  known 
to  exist,  but  practically  nothing  is  known  of  its  extent. 

In  a  previous  chapter  it  has  been  noted  that  changes  in 
elevation,  especially  along  the  shore,  are  taking  place. 
The  real  extent  of  the  continents,  therefore,  is  not  appar- 
ent ;  in  many  places  it  comprises  an  area  somewhat  greater 
than  the  part  above  water.  Each  is  surrounded  by  a 
margin,  varying  from  a  few  rods  to  one  hundred  miles  or 
more,  upon  which   the   sea  is  comparatively  shallow ;  be- 


LAND   AND   WATER  43 

yond  this  margiu  the  surface  slopes  rather  abruptly  into 
deep  water. 

The  submerged  margiu  is  very  generally  considered  a 
part  of  the  continent.  The  depth  of  water  along  its  extent 
varies,  and  in  places  the  margin  itself  reaches  above  sea- 
level.  The  margin  of  each  continent  is  more  or  less  con- 
tinuous, and  forms  a  high  surface  in  comparison  with  the 
surrounding  sea-bottom.  It  is  usually  called  the  continental 
shelf. ^  The  map  on  p.  45  shows  both  the  highland  and  the 
lowland  regions  of  each  continent  and  also  its  submerged 
shelf :  facing  what  ocean  are  the  highlands  ? — the  lowlands  ? 
Where  is  the  continental  shelf  widest  ? — on  which  side  of 
North  America  has  it  the  greatest  width  ?  The  highlands 
are  represented  by  the  area  above  the  level  of  2,000  feet : 
compare  the  extent  of  highlands  and  lowlands  in  each  con- 
tinent ;  in  North  America.  Are  the  highlands  continuous 
or  broken  ?  Each  one  is  a  great  plateau  rimmed  and  trav- 
ersed by  lofty  mountains.  About  one-fifth  of  the  Austra- 
lian, two-fifths  of  the  American,  and  three-fifths  of  the 
Asian  continent  are  above  the  2,000-foot  contour. 

The  altitude  of  the  highest  regions  of  the  continents 
differs  much.  The  greater  elevations  of  North  America 
are  from  one  to  one  and  a  half  miles  above  sea-level  ; 
those  of  South  America,  about  two  miles ;  and  the  highest 
parts  of  Asia  are  more  than  three  miles  above  sea-level. 
The  mountains  that  rim  or  surmount  the  highlands  are 
much  higher — in  many  instances  about  twice  as  high. 

The  slopes  toward  the  Arctic  and  Atlantic  Oceans  are 
long  and  gentle ;  how  does  this  fact  compare  with  the 
slopes  of  the  Pacific  and  Indian  Oceans  ?  As  a  rule,  the 
lowland  regions  are  more  nearly  level  than  the  highlands. 
On  which  side  of  the  eastern  continent  are  its  principal 
lowlands  ?  On  which  side  of  the  American  continent  are 
they  situated? 


& 


d). 


THE  WORLD 

showing 

ELEVATION  OF  LAND 

and 

DEPTH  OF  WATER. 


<:5i 


&' 


'f> 


T.Ivvation  ul'  Land 

I    20,000  Feet  or  over 

I    10,000  -  20,000  Feet 

1,000  -  10,000     •' 

0-    1,000     " 

telow  sea  level 

Depth  uf  Water 

0  -   1,000  Fathoms 
1,000  -   2,000     " 
2,000-    4,000     " 
4,000  or  over 


46 


PHYSICAL   GEOGRAPHY 


The  mean  elevation  of  the  land  varies  considerably  in 
the  various  continents.  If  their  surfaces  were  levelled  off 
Australia  and  Europe  would  be  not  far  from  one  thousand 
feet  high ;  North  America  and  Africa  about  two  thousand 
feet ;  and  Asia  nearly  three  thousand  feet.  Africa  would 
be  probably  a  little  higher,  and  South  America  not  quite 
so  high  as  North  America. 

In  a  few  instances  there  are  depressions  in  the  land  be- 
low sea-level.  The  surface  of  the  Caspian  Sea  is  eighty-four 
feet  below  that  of  the  Mediterranean  ;  the  Dead  Sea,  situ 
ated  in  a  gash  north  of  the  Red  Sea,  is  thirteen  hundred  feet 
below  sea-level.  There  are  two  small  dej^ressions  in  North 
America,  north  of  the  Gulf  of  California ;  and  two  or  three 
in  Africa,  south  of  the  Atlas  Mountains.  It  is  not  unlikely 
that  these  were  former  arms  of  the  sea  that  were  severed 

from  the  main  body. 

Islands.— The  islands 
have  an  aggregate  area 
of  about  three  million 
square  miles,  or  about 
one-seventeenth  of  the 
entire  land  siu'face  of  the 
earth.  The  majority  of 
them  are  situated  on  the 
continental  plateau,  and 
are  at  no  gi*eat  distance 
from  the  continents  to 
which  they  belong.  Many 
of  them  are  partly  sub- 
merged ranges  of  moun- 
tains that  are  parallel  to 
the  maritime  ranges  of 
the  continent,  or  that  ex- 
tend from  it.     Find  two 


itaUtrom*^   West    ^ 


A  STRETCH  OF  THE  COAST  OF  NORWAY 

The  coast,  deeply  indented  with  fjords,  is  bordered 
by  many  thousand  rocky  islets. 


LAND   AND   WATEE  47 

such  chains  near  the  American  continent,  two  near  the 
Asian  continent.  Islands  of  this  character  are  usually 
called  continental  islands  ;  and  the  reason  is  ol)vioas. 

In  a  few  instances,  here  and  there,  are  islands  far  distant 
from  any  large  body  of  land.  There  is  no  doubt  about 
the  origin  of  some  of  them ;  they  consist  of  the  lava  that 
has  been  ejected  from  volcanoes.  In  some  instances  these 
islands  are  solitary,  as  Jan  Mayen  and  St.  Helena  ;  in 
others  they  form  a  chain,  as  the  Hawaiian  group. 

In  the  Pacific  Ocean  there  is  a  large  area  in  which  isl- 
ands are  so  numerous  that  the}'  form  the  well-defined  grand 
division  Polynesia;  find  the  meaning  of  this  word  from 
the  dictionary.  These  islands  occur  in  quite  regular  chains 
that  are  roughly  parallel  in  direction ;  they  are  therefore 
thought  to  be  the  higher  summits  of  submerged  mountain- 
ranges.  In  some  instances  a  volcanic  peak  is  in  sight,  but 
for  the  greater  part  the  position  of  each  peak  is  marked 
by  the  reef  of  coral  growth  that  encircles  it.  The  islands 
themselves  are  popularly  known  as  coycCl  islands.^ 

It  has  been  inferred  that  the  coral  polyps  began  their 
growths  ou  the  slopes  of  the  volcanic  peaks,  and  that  the 
latter  gradually  subsided  until  they  were  covered  by  the 
sea.  But  while  the  peak  Avas  slowly  sinking  the  coral 
polyps  steadily  built  their  reefs  upward,  keeping  the  top 
always  even  with  the  wash  of  the  waves.  This  opinion, 
first  made  prominent  ])y  Darwin,  is  borne  out  by  the  fact 
that,  while  the  coral  poh'p  cannot  live  more  than  twenty 
fathoms  below  the  surface  of  the  sea,  the  reefs  sometimes 
extend  almost  vertically  to  a  dei)th  of  several  hundi'ed 
fathoms. 

A  peculiar  feature  about  many  of  these  islands  is  their 
form.  As  a  rule  each  consists  of  an  irregular  ring  of  reef 
matter,  broken  and  tossed  up  by  the  waves,  surrounding 
shallow  water.     The  reef  is  called  an  atoll ;  the  enclosed 


48 


PHYSICAL   GEOGRAPHY 


water  a  lagoon.    Usually  the  atoll  is  broken  in  one  or  more 
places,  and  in  many  instances  the  lagoons  form  good  har- 

^  bors.     The  reef  is  rarely  more  than  a 

/'/>■■:::       \  few  feet  high,  and  its  vegetation  is  con- 

j      f^v'      \  fined  to  a  few  species,  mainly  of  palms. 

Ii  (1  \  The  Sea. — The   sea   covers  more 

/  I    j(  \         than    half   the    northern    and   about 

i         ^  i  0:)j  \       seven  eighths  of  the  southern  hemi- 

sphere. Although  the  area  it  covers 
is  continuous,  it  is  separated  by  the 
continents  into  great  divisions  called 
oceans.  Name  them.  Which  one  is 
nearly  enclosed  ?  Compare  the  At- 
lantic in  shape  with  the  others.  For 
convenience,  the  polar  circles  are 
taken  as  the  boundaries  of  the  polar 
oceans,  and  the  equator  convention- 
ally divides  the  two  largest  oceans 
into  nortliern  and  southern  divisions. 
Which  of  the  oceans  is  nearly  land- 
locked ?  At  what  place  do  the  Pacific 
and  Arctic  Oceans  meet?  tlie  Atlan- 
tic and  Pacific  ?  the  Atlantic  and 
Indian  ?  the  Atlantic  and  Arctic  ? 
The  Pacific  Ocean  comprises  about  one-lialf  the  entire 
Sea ;  the  Atlantic  about  one-quarter.  The  shore  line  of 
the  latter,  however,  is  considerably  longer  ;  explain  why. 
Why  are  not  the  polar  oceans  important  routes  of  traffic  ? 
On  a  globe  trace  a  northwest  passage  from  London  to 
India ;  why  is  not  such  a  passage  feasible  as  a  trade  route  ? 
In  general,  the  average  depth  of  the  oceans  varies  with 
their  size — the  larger  the  ocean  the  greater  its  depth.  The 
Pacific  is  about  2,500  fathoms,  the  Atlantic  and  Indian  not 
far  from  2,000  fathoms.     The  polar  oceans  are  shallower, 


A  GROUP  OF  CORAL 
ATOLLS  SURROUNDED 
BY  A  BARRIER  REEF 


LAND   AND    WATER  49 

but  not  enough  is  known  about  their  depth  uj^on  which  an 
average  can  be  con)puted.  The  greatest  ocean  depths  are 
much  in  excess  of  the  average  depths.  There  is  a  large 
3,000-fathom  area  in  the  north  Pacitic — compare  it  Avith 
Australia  in  size — and  several  smaller  areas  in  the  Atlan- 
tic and  Indian  Oceans.  There  are  also  several  4,000-fatliom 
and  at  least  two  small  5,000-fathom  aieas ;  describe  their 
positions.^  The  greatest  depth  of  the  sea,  it  is  seen, 
scarcely  surpasses  the  height  of  the  loftiest  mountain 
peak  ;  yet  while  four-fifths  of  the  sea  basin  is  six  thou- 
sand feet  lower  than  sea-level,  less  than  a  tenth  of  the  land 
reaches  six  thousand  feet  above  it. 

The  floor  or  bod  of  the  sea  is  by  no  means  so  irregular 
as  the  surface  of  the  land ;  and,  the  vicinity  of  the  coral 
islands  and  the  continental  shores  excepted,  no  steep  slopes 
or  abrupt  changes  of  level  are  known  to  exist.  The  sound- 
ings made  for  the  telegraph  cables  disclosed  no  slopes  nor 
inclines  too  steep  for  a  railway  grade.  After  deep  water 
was  reached,  the  soundings  for  the  Atlantic  cable  of  1866 
did  not  vary  more  than  seven  or  eight  hundred  feet  in  two 
thousand  miles. 

Arms  of  the  Sea. — In  various  places  the  sea  extends  to 
a  considerable  distance  within  the  general  outlines  of  the 
continents,  forming  the  bodies  or  arms  called  seas,  gulfs, 
bays,  sounds,  straits,  etc.  Many  of  the  smaller  coves  and 
estuaries  are  shore  formations,  having  been  made  or 
shaped  by  the  action  of  waves  or  by  currents  of  water. 
The  larger  arms,  however,  are  structural,  and  have  resulted 
from  upheaval  or  depression  of  the  continent,  or  of  some 
part  of  it. 

The  liorders  of  a  continent  may  be  flanked  by 'lofty 
highlands,  and  the  trend  of  the  coast  usually  conforms  to 
the  trend  of  the  ranges.  Tlius,  the;  bend  that  gives  the 
west  coast  of  Africa  its  sliajic  also  gives  a  similar  form  to 


50 


PHYSICAL   GEOGRAPHY 


the  Gull"  of  Guinea.  Where  paraHel  rauges  extenci  sea- 
ward, or  form  an  angle  witli  the  coast,  the  sea  usually  en- 
ters the  valley  to  some  distance  between  them.  On  a  map 
of  North  America,  note  the  position  of  the  Gulf  of  Cali- 
fornia, and  Puget  Sound  ;  on  a  map  of  Europe,  the  Adri- 
atic Sea.  Note  similar  examples  along  the  west  coast  of 
Asia.  Compare  the  coast  lines  of  the  grand  divisions 
with  reference  to  indentations.  Which  has  the  longer 
coast  line — Europe  or  Africa  ? 


A    KO(  K  bi)L  NU    I  ()  'lM       1  111     (.  1(.  L  )l  -1     (  U  \     I 

Unfit  for  commerce  and  a  menace  to  navigation. 

Almost  any  partly  enclosed  portion  of  an  ocean  is  called 
a  sea,  and  the  Caribbean  and  North  Seas  are  examples  of 
a  type  of  enclosed  waters.  There  is  another  type,  how- 
ever, that  is  even  more  remarkable  because  practically 
land-locked.  Of  this  type  the  Mediterranean  is  an  exam- 
ple, and  such  arms  of  the  ocean  are  now  often  called  7nedi- 
terraneans.  The  Gulf  of  Mexico  is  properly  included  in 
this  class.     Nearly  all  the  larger  arms  of  the  sea  are  de- 


LAND    AND    WATER 


51 


pressed  parts  of  tlie  continents,  or  of  the  plateau  on  wliicli 
tliey  are  situated. 

Coast  Forms. — The  study  of  ahnost  any  good  map  of 
a  continent,  or  of  any  considerable  part  of  its  shore  out- 
lines, shows  that  various  parts  of  the  coast  differ  materially. 
Compare,  for  instance,  the  coasts  of  Maine  and  Florida  ; 
of  the  Chesapeake  Bay  and  southern  California.  The  illus- 
trations on  pp.  46  and  52  are  examples  of  shore  forms. 
One  of  them  is  a  rock-bounil  coast  deeply  indented  with 
fjords  and  hemmed  in  by  rocky  islets.  This  coast  has 
been  worn  and  frayed  by  the  action  of  sheets  of  ice,  but  it 
has  also  subsided  until  the  valleys  are  submerged  by  the 
sea.     Name  the  various  coasts  that  resemble  it. 


A   CI.IFF-CIRT   COAbl,    sAN  JUAN,    HUI-.K1(>    RICU 

In  the  illustiaticm  on  p.  52,  the  plain  bordering  the  sea 
dij)s  so  gently  below  sea-level  that  tlie  water  is  shallow  half 
a  mile  or  more  from  the  shore.  The  drag  of  the  waves  roll- 
ing ill  and  cond)iiig  on  the  coast  picks  up  sand  and  rock 
waste  brought  down  by  muddy  streams  and  piles  it  in  the 
form  of  long  spits  and  beaches  at  a  little  distance  from  the 
shore.''     Find  other  coasts  that  resemble  it. 


52 


PHYSICAL   GEOGRAPHY 


Along  many  parts  of  the  coast  the  sea  seems  to  be  en- 
croaching on  the  land,  and  the  Avaves  beat  against  the 
shore,  breaking  it  away  until  there  is  a  high  cliff  with  a 
narrow  beach  at  its  foot.  A  considerable  extent  of  the 
California  coast  is  bordered  by  sea-cliffs,  and  they  occur 

here  and  there  along  the 
North  Atlantic  coast,  as 
at  the  coast  of  Newport, 
Rhode  Island. 

Coral  formations   are 
very  important  factors  in 
shore  lines.     On   shore 
they  are  called  frinying 
reefs ;  fartlier  out,  har- 
rier reefs.     Almost  the 
entire  east  coast  of  Aus- 
tralia is  shut  off  from 
open  communication  by 
a  barrier  reef  more  than 
twelve    hundred     miles 
long.     There  are  a  few 
channels  across  the  reef, 
but  the  latter  is  a  great 
obstacle    to    commerce. 
Fringing  reefs  occur  on 
the  south  coast  of  Flor- 
ida,  and  they  are  per- 
haps the  most  common 
examples  of  coral  formation.     They   are    common    along 
the  shores  of   the    Bahama  Islands,  and  occur  here  and 
there  along  the  Hawaiian  coast. 

Coral  growths  are  confined  to  warm,  littoral  waters,  and 
the  reef-building  ]3olyp  is  limited  to  waters  whose  temper- 
ature does  not  fall  beloAv  25°  (67°  F.).     Absolutely  clear 


A  STRETCH  OF  NORTH  CAROLINA  COAST 


The  barrier  beaches  nearly  enclose  the  coast ;  the 
inlets  arc  kept  deep  enough  for  navigation  by  the 
tidal  currents. 


LAND   AND    WATER  53 

water  is  requisite,  aud  for  this  reason  coral  reefs  are  rarely 
found  aloug  the  shores  of  coutinents,  aud  never  within  the 
reach  of  river  sediments. 

Coast  Outlines  and  Civilization. — The  coast  forms  of 
a  country  have  not  a  little  bearing  on  its  prosperity  and 
its  enlightenment  as  well.  A  coast  with  good  harbors  in- 
vites commerce  and  iutercommuuication.  Along  the  North 
Atlantic  coast  of  the  United  States,  where  a  rugged  surface 
slopes  abruptly  below  sea-level,  good  harbors  are  nume- 
rous. The  same  conditions  prevail  on  the  coast  of  Europe. 
Of  two  regions,  one  having  good,  the  other  poor  harbors, 
commerce  aud  intercommunication  will  seek  the  former. 
Africa  and  South  America  have  but  very  few  good  harbors, 
and  to  this  fact  tlie  half -savage  condition  of  the  native 
peoples  is  largely  due.  The  great  stride  in  the  progress 
of  the  Japanese  people  was  begun  when  they  opened  their 
ports  to  foreign  trade. 

QUESTIONS  AND  EXERCISES-— How  have  good  harbors  affected 
the  progress  of  the  English  people  .•*  What  has  been  the  effect  of  closed 
ports  on  the  Chinese  ? 

Compare  the  commerce  of  the  North  Atlantic  coast  of  the  United 
States  with  that  of  the  South  Atlantic  coast.  To  which  type  does  each 
ot  these  coast  forms  belong  ?  Where  are  most  of  the  large  seaports  of 
the  Atlantic  coast  of  the  United  States  ?  Explain  the  reason  for  their 
location. 

Why  should  Australia  be  considered  a  continent  rather  than  an 
island  ? 

Does  the  cutting  of  the  Suez  Canal  give  Africa  any  insular  properties 
that  it  did  not  possess  before  ? 

Make  a  list  of  the  principal  mediterranean  seas  of  the  world. 

Mention  several  instances  in  which  peninsulas  enclose  waters  so  as 
to  form  gulfs  or  bays. 

From  a  good  map  of  the  British  Isles  find  the  names  used  as  syno- 
nymes  of  "  cape  "  and  "  strait." 

Find  the  centre  of  each  hemisphere  on  p.  40. 

Study  the  position  of  the  submerged  part  of  the  continents  on  the 
map,  pp.  45-46- 


54  PHYSICAL   GEOGKAPHY 


COLLATERAL    READING 

Dana. — Manual  of  Geology,  pp.  145-152. 

Redway. — New  Basis  of  Geography.     Chapter  IV. 

Shaler. — Sea  and  Land,  pp.  187-232. 

United  States  Geological  Survey. — Norwich  and  New 
London  Sheet  (drowned  valleys)  ;  Sandy  Hook  and  Barnegat 
Sheets  (spits  and  barrier  beaches;  ;  Port  Washington  Sheet 
(cliffs). 

NOTES 

^  It  is  commonly  asserted  that  the  same  amount  of  water  ex- 
ists on  the  earth  at  the  present  time  as  during  remote  geological 
periods.  This  is  doubtless  true,  but  it  is  also  true  that  not  all 
the  water  is  in  the  same  form  now  as  in  prior  times.  When 
the  earth  was  younger  there  was  much  water  in  a  liquid  form 
that  is  now  chemically  combined  with  various  mineral  elements. 
Nearly  all  the  minerals,  especially  those  in  a  crystalline  form, 
contain  notable  proportions  of  water  in  combination. 

-  This  separation  of  the  land  masses  has  been  aptly  called 
the  "zone  of  fracture."  The  isthmus  of  Panama  is  scarcely 
thirty  miles  wide  and  the  isthmus  of  Suez  is  only  one  hundred 
miles  across.  Yet  these  two  necks  of  land  are  all  that  connect 
the  divisions  of  each  continent.  That  is,  twenty-five  thousand 
miles  of  open  navigation  are  obstructed  by  less  than  one  hundred 
and  thirty  miles  of  land.  Even  these  barriers  are  disappearing 
because  of  canals  either  completed  or  projected. 

^  It  is  now  the  custom  to  restrict  the  latter  term  to  the  largest 
land  masses,  but  it  is  sometimes  more  convenient  to  apply  it  to  a 
grand  division.  Europe  and  Asia  are  also  called  continents,  but 
the  only  real  boundary  that  separates  them  is  the  desert  high- 
land that  separates  western  from  oriental  civilization.  Physically 
it  is  better  to  treat  Eurasia  as  a  whole — politically  and  histori- 
cally the  two  divisions  are  best  considered  separately. 

*  This  margin  is  also  called  the  continental  plateau,  the  conti- 
nental border,  and  the  sxibmerged  border. 

^  The  coral  polyp  is  a  zoophyte  form  of  marine  animal  growth 
not  unlike  a  tree  with  its  branches.     The  mouths  of  the  polyp 


LAND    AND    WATER  55 

coujpletely  cover  its  upper  surface  in  much  the  same  manner  as 
the  flowers  of  the  ht)llyliock  or  mullein  cluster  about  the  stem. 
In  a  single  community  the  growth  of  the  polyp  is  ehietly  upward, 
but  where  the  communities  are  thickly  clustered,  their  branches 
interlock  and  finally  form  a  compact  mass.  The  living  portion 
of  a  coral  is  found  at  the  surface  of  the  water  or  a  few  feet  below 
it  ;  the  dead  portion  may  extend  a  hundred  fathoms  or  more  be- 
low the  surface. 

^  The  deepest  soundings  so  far  obtained  are  4,  G55  fathoms  by  the 
U.  S.  S.  Tuscarora,  east  of  Japan,  in  an  area  now  known  as  Tus- 
carora  Deep  ;  5,147  fathoms,  one  hundred  miles  E.  N.  E.  of  Sun- 
day Island  ;  and  5,150  fathoms  a  few  leagues  east  of  Macarthy  Isl- 
and, not  far  from  the  Kermadec  group.  The  two  last  were  made 
by  Commander  Balfour,  H.  M.  S.  Penguin.  North  of  Puerto  Rico 
a  sounding  of  4,051  fathoms  has  been  obtained.  The  cable  ship 
Nero  reported  a  sounding  of  5,200  fathoms  east  of  the  Hawaiian 
Islands.  Formerly  deep  sea  soundings  were  made  with  heavy 
Manila  rope,  and  in  very  deep  water  it  was  impossible  to  tell 
when  the  sinker  had  reached  bottom.  With  tlie  method  perfected 
by  Admiral  Belknap  and  Captain  Sigsbee,  steel  piano  wire  takes 
the  place  of  the  rope.  The  wire  carries  at  its  lower  end  a  sinker 
which  detaches  itself  on  touching  bottom,  at  tlie  same  time  clos- 
ing a  cup  that  secures  a  specimen  of  the  bottom.  Very  few  of 
the  deep-sea  soundings  made  prior  to  1870  are  now  considered 
trustworthy. 

^Marine  currents  frequently  attempt  to  carry  away  the  rock 
waste  piled  up  by  the  waves,  and  between  the  two  it  is  dragged 
into  a  curved  form  making  a  Jiook.  Sandy  Hook,  New  .Jersey, 
is  an  example,  and  similar  examples  are  found  along  the  shorep 
of  Marthas  Vinevard  and  Nantucket. 


CHAPTER  IV 

THE    EESULTS    OF    SLOW  MOVEMENTS   OP   THE  EOCK 
EN^^LOPE  :    PLAINS,   PLATEAUS,    AND   MOUNTAINS 

The  larger  vertical  forms  of  the  land  are  the  results  of 
the  slow  movements  of  the  rock  envelope.  Any  consider- 
able area  of  laud  but  little  liigher  than  sea-level  is  called 
a  plain ;  if  considerably  higher,  a  plateau ;  if  wrinkled, 
folded,  and  broken,  a  mountain  system.  There  is  no  fixed 
elevation  at  which  an  area  ceases  to  be  a  lowland,  or  vice 
versa,  but  in  general,  surfaces  more  than  two  thousand  feet 
above  sea-level  are  called  highlands,  while  those  of  less  alti- 
tude are  lowlands. 

As  a  rule,  the  various  features  that  constitute  topogra- 
phy are  distinct  one  from  another  ;  but  in  many  instances 
lowlands  gradually  increase  in  altitude  and  become  high- 
lands ;  an  almost  imperceptible  swell  in  a  level  plain  may 
develop  into  a  cliff  or  a  ridge  ;  and  a  mountain-range,  little 
by  little,  may  lose  its  characteristic  form  among  other 
features  of  the  landscape.  So  it  often  happens  that  a  sin- 
gle topograpliic  form  may  have  the  character  of  several 
kinds  of  relief. 

Plains. — Any  level  or  nearly  level  stretch  of  land  is 
commonly  called  a  plain.  Most  plains  are  lowlands,  but  in 
a  few  instances  the  name  is  applied  to  surfaces  that  are 
more  than  six  thousand  feet  above  sea-level— au  elevation 
considerably  greater  than  that  of  some  mountain-ranges. 
The  plain  east  of  the  Rocky  Mountains  is  an  example ; 

56 


PLAINS,    PLATEAUS,    AND    MOUNTAINS       57 

it  is  higher  than  the  crests  of  the  Appalachian  Mountains, 
and  about  as  high  as  the  highest  ]ieaks. 

Plains  are  variously  named.  The  grassy  plains  of  the 
New  World  were  named  savannas  by  the  Spanish,  and 
prairies  by  the  French — both  of  which  names  are  very 
commonly  employed.  In  South  America  the  vast  plains 
of  Argentina  are  called  pampas  ;  the  grassy  plains  of  the 
Orinoco,  llanos  ;  and  the  forest-covered  plains  of  the  Ama- 


A   ROLLING   PLAIN,  VIRGINIA 

The  forestry  h  drficiciil,  aihl  the  soil  only  luojci  alcly  fertile. 

zon,  silvas}  In  Eurasia,  the  vast  plains  that  almost  girdle 
the  Arctic  Ocean  arc  known  as  sleppcs,  their  frozen,  swampy 
coast  fringe  Ijeiiig  known  as  tundras.  In  England  and 
Sc(4laiid  the  terms,  iii('<i(h>ir,  heaf/i,  and  moor,  are  used. 

Origin  of  Plains. — Most  ])l;ii)is  Jiave  been  formed  by 
the  acti(m  of  wat(!r,  or  have  r('C(^iv(Ml  tluiir  surface!  contigu- 
ratiou  by  it.     If  shaped  by  comparatively  still  water  they 


58  PHYSICAL   GEOGRAPHY 

are  known  as  marine  or  lacustrine  plains  ;  the  former  being 
old  sea-bottoms ;  the  latter  lake  basins.  If  formed  of  sedi- 
ments deposited  by  running  streams  they  are  alluvial 
plains  ;  if  levelled  off  by  moving  ice,  diluvial  plains  ;  if  on 
the  margin  of  the  sea  or  a  lake,  coast  plains. 

Marine  and  lacustrine  plains  constitute  by  far  the  greater 
area  of  the  lowland  siirface  of  the  earth.  Originally  old 
sea  or  lake  bottoms,  their  surfaces  are  level,  because  the 
sediments  forming  them  were  deposited  in  still  water.  In 
some  instances  the  floor  was  filled  and  levelled  off  by  the 
remains  of  minute  animals  ;  in  others  b}^  dead  and  decay- 
ing vegetation. 

In  time  these  old  bottoms  were  raised  above  water-level 
and,  if  their  surfaces  were  not  wrinkled  and  folded,  they 
constitute  the  plains  of  to-day.  Thus,  the  larger  part  of 
the  Great  Central  Plain  of  North  America  is  an  old  sea- 
bottom,  and  so,  too,  is  most  of  the  great  northern  plain  of 
Eurasia.  Of  lacustrine  plains,  one  of  the  finest  exam^iles 
is  the  valley  of  Bed  River  of  the  North.  This  plain  re- 
sulted from  the  draining  of  a  lake,  and  was  so  recently 
formed  that  its  surface  has  scarcely  been  notched  by  the 
river  that  now  imperfectly^  drains  it. 

The  plain  surrounding  the  Caspian  Sea  is  an  excellent 
example  of  a  plain  in  the  process  of  formation.  On  the 
northern  side,  the  gradual  shrinkage  of  the  lake  has  left  a 
plain  more  than  two  hundred  miles  wide,  and  when  at 
length  the  lake  disappears,  a  broad,  wind-swept  plain  will 
take  its  place.^  The  Talley  or  basin  of  Great  Salt  Lake 
possibly  is  passing  through  a  similar  period  of  growth 
and  development. 

Alluvial  plains  are  usually  best  developed  along  the 
lower  courses  of  rivers,  although  they  exist  in  narrow 
reaches  along  almost  the  entire  length  of  the  stream.  The 
bottom-lands  of  the  lower  Mississippi  and  the  Danube ; 


PLAINS,    PLATEAUS,    AND   MOUNTAINS       59 


the  mazy  deltas  of  tlie  Nile  and  the  Ganges-Brahmaputra, 
and  the  broad,  fertile  plains  of  the  Po  are  examples/ 
Name  other  illustrations. 

The  surface  of  a  coast  plain  is  made  level  by  the  action 
of  the  waves,  and  if  an  uplift  of  the  surface  is  taking  place, 
the  j)lain  gets  gradually  wider  and  wider  as  successive  por- 
tions of  the  sea-bottom  are  brought  to  the  surface.  The 
coast  plain  along  the  South  Atlantic  and  Gulf  coast  is  an 


A  very  JcitiU-  pi. Ill  u- 


iJ<iuhl,-  I'oicsl  growth. 


excellent  example.'  Much  of  the  material  of  which  it  is 
composed  is  sodiiuent  brought  down  by  the  rivers,  but  the 
waves  have  been  the  chief  ag(!iit  in  building  it.  Through- 
out its  whole  ext(!nt  it  is  but  little  higher  than  tide-water. 
The  line  along  which  the  const  [)]ain  joins  the  older  land  is 
marked  by  a  rather  abrupt  slo])e  called  the  "Fall  Line," 
and  in  most  jjlaces  th(!  lin*;  wluire  they  meet  is  quite  distinct. 


60  PHYSICAL    GEOGRAPHY  . 

Most  of  the  rivers  are  navigable  to  the  Fall  Line,  and  along 
the  eastern  side  coast  a  line  of  cities  marks  the  junction. 

Almost  every  body  of  land  is  surrounded  by  a  coast 
plain  ;  indeed  its  formation  and  growth  necessarily  follows 
the  denudation  or  wasting  of  the  land.  Rock  waste  is  con- 
stantly being  carried  to  sea-level  by  running  waters,  but 
beyond  this  point  it  can  go  little  or  no  farther  ;  so  it  is 
distributed  along  the  shore  and  levelled  off  by  the  waves. 
In  most  instances  slow,  vertical  movements  of  the  rock  en- 
velope are  concerned  in  the  formation  and  development  of 
coast  plains,  but  in  many  cases  rivers,  waves,  and  tidal  cur- 
rents divide  the  work  among  themselves. 

In  various  places  surfaces  formerly  rugged  have  been 
levelled  off  by  the  action  of  the  sheet  of  ice  that  once  cov- 
ered portions  of  Europe  and  North  America.  Much  of  the 
northern  part  of  the  United  States  received  the  configura- 
tion of  its  surface  by  this  process  ;  the  moving  sheet  of 
ice  scoured  off  the  rugged  parts  and  filled  the  depressions 
with  the  material  removed.'' 

Distribution  of  Plains. — Alluvial  and  lacustrine  plains, 
of  course,  are  incidents  in  the  physiography  of  rivers  and 
lakes  ;  and  coast  plains  are  formed  on  nearly  all  shores. 
The  great  marine  plains  of  the  world  are  mainly  on  the 
slopes  of  the  Arctic  and  the  Atlantic  Ocean.  The  most 
extensive  plain  of  the  world  is  that  which  forms  the 
northern  slope  of  Eurasia.  From  east  to  west  it  stretches 
a  distance  of  about  nine  thousand  miles  ;  from  north  to 
south,  about  three  thousand  miles.  In  Asia  it  is  high  and 
rolling  ;  in  Europe  the  greater  part  of  its  extent,  how- 
ever, is  low  and  comparatively  level.^ 

In  the  New  World  the  great  continental  plain  extends 
from  the  Arctic  Ocean  to  the  Gulf  of  Mexico,  and  there  is 
an  apparent  extension  from  the  Caribbean  Sea  southward 
through   South   America.     Its    continuity    is   broken    by 


PLAINS,    PLATEAUS,    AND   MOUNTAINS       Gl 

occasional  ranges  and  arms  of  the  sea.  It  presents  cer- 
tain marked  contrasts  to  the  plain  of  the  Asian  Continent. 
The  latter  extends  east  and  west ;  the  former,  north  and 
south.  The  latter  is  a  margin  of  the  continent ;  the  for- 
mer is  an  interior  plain,  bordered  by  mountain-ranges. 

Physiographic  Aspect  of  Plains. — Although  water  is 
the  chief  agent  in  the  formation  of  plains,  it  is  likewise  the 
chief  factor  in  their  destruction.  From  the  moment  a  plain 
comes  into  existence,  storm  waters  and  running  streams  be- 
gin to  carve  channels  in  its  surface.  These,  extending  in 
area,  carry  the  greater  part — perhaps  all  the  surface  mate- 
rial away.^  A  plain  thus  channelled  is  said  to  be  "  dissect- 
ed." The  coast  plain  of  much  of  the  South  Atlantic  and 
Gulf  coast  is  young,  especially  near  the  sea.  Its  slope  is 
so  gentle  that  the  streams  have  not  yet  carved  their  chan- 
nels to  any  great  depth. 

The  plains  bordering  Lakes  Erie  and  Ontario  show  signs 
of  greater  age.  The  streams  have  accomplished  a  consid- 
erable dissection  and  the  channels  are  comparatively  deep. 
The  "  Bad  Lands  "  of  South  Dakota  and  Nebraska  are 
remnants  of  an  old  lacustrine  plain  that  has  been  so  greatly 
dissected  that  the  region  is  well-nigh  impassable  through- 
out much  of  its  extent. 

Economic  Value  of  Plains. — Because  of  their  com- 
paratively level  surface,  plains  are  more  accessible  to 
commerce  than  mountainous  regions.  Hallways  can  be 
built  across  them  at  the  minimum  of  cost,  and  the  rivers 
that  traverse  them  are  usually  navigable. 

More  than  this,  the  soil  of  plains  is  usually  deep  and 
easily  cultivated.  Therefore  they  are  capable  of  support- 
ing a  denser  pojjulation  than  mountainous  regions.  In 
renjote  times  the  alluvial  plains  of  the  Nile  and  of  Meso- 
potamia were  the  seats  of  dense  population  and  vast  in- 
dustries.    In  later  times  the  plains  of  Europe  and  of  the 


C2  PHYSICAL  GEOGRAPHY 

Uuited  States  have  become  the  great  producers  of  wealth. 
It  may  be  said,  therefore,  that  the  greater  part  of  the  world's 
wealth  aud  power  is  centred  iu  the  plains  of  the  temperate 
zones.  Only  a  small  fraction  of  the  world's  population  lives 
above  the  altitude  of  2,000  feet,  and  but  few  of  the  great 
cities  are  more  than  six  hundred  feet  above  sea-level. 

Plateaus. — Almost  any  broad  extent  of  country  having 
an  elevation  of  more  than  a  few  hundred  feet,  and  an  ir- 
regular or  dissected  '  surface,  is  popularly  called  a  plateau. 
The  name,  originally  meaning  "  Hat,"  or  "  level,"  has  ac- 
quired a  signification  almost  the  opposite.  A  plateau  of 
small  area  is  usually  called  a  mesa,  a  table-land,  or  a  tahle- 
mountaia,  according  to  its  general  form  aud  structure. 

Like  most  other  elevations  of  the  earth's  surface,  pla- 
teaus are  the  result  of  a  gradual  uplift  of  parts  of  the  rock 
envelope.  Most  of  the  great  plateaus  of  the  earth  are 
rimmed  by  lofty  mountain-ranges,  and  their  surfaces  are 
generally  traversed  by  ridges  and  valleys.  Thus,  the  pla- 
teau region  of  western  North  America,  nearly  a  mile  and 
a  half  high,  is  bordered  by  the  lofty  ranges  of  the  Eocky 
Mountains;  and  Sierra  Nevada  systems  ;  the  great  Boliv- 
ian plateau  is  margined  by  the  highest  summits  of  the 
Andes  ;  aud  the  loftiest  plateau  in  the  world,  that  of  Tibet, 
is  enclosed  by  some  of  the  loftiest  ranges  of  the  earth. 

Mesas  and  table-lands  are  generally  the  result  of  ero- 
sion, or  unequal  weathering.  The  top  of  the  mesa  is  com- 
monly a  layer  of  rock  resting  upon  softer  substance.  The 
latter  is  protected  from  the  action  of  the  elements  by  the 
harder  material  and,  in  time  a  table-land  is  formed.  With- 
out the  hard  cap  the  surface  would  have  been  rounded  off, 
leaving  a  hill  instead  of  a  mesa.  As  a  rule,  mesas  and 
table-lands  are  the  outlying  or  isolated  remnants  of  pla- 
teaus. They  are  noticeable  objects  because  of  their  flat  toj)s 
and  the  steep  cliffs  or  escarpments  that  form  their  slopes. 


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Echo  Cliffs 


64  PHYSICAL   GEOGRAPHY 

Distribution  of  Plateaus. — Most  of  the  high  plateaus 
are  in  the  great  highlands  that  radiate  from  north  circum- 
polar  regions  ;  they  face  the  Pacific  and  Indian  Oceans, 
A  series  of  lesser  highlands  borders  the  Atlantic  Ocean, 
and  these  also  contain  plateaus.  Although  the  plateaus 
have  each  a  more  or  less  definite  outline  they  cannot  al- 
ways be  considered  apart  from  the  highlands  to  which 
they  belong.  In  places  where  the  highlands  border  the 
sea,  the  plateaus  may  take  the  form  of  peninsulas ;  name 
several  examples  on  the  map  of  Asia. 

Among  the  plateaus  of  the  Asian  Continent,  that  of 
Tibet  is  remarkable  for  its  size  and  elevated  surface,  near- 


A   DISSECTED   PLATEAU,  JOHN   DAY   VALLEY,  OREGON 

The  shed  of  lava  at  the  surface  has  been  removed  here  and  there,  leaving  a  series  of  mesas. 

ly  three  miles  above  sea-level ;  by  what  ranges  is  it  partly 
enclosed  ?  To  the  westward  are  the  Pamirs,  a  series  of 
grassy  plateaus,  like  the  "parks  "  of  Colorado,  about  three 
and  a  half  miles  above  the  sea.  In  North  America,  the 
plateaus  of  the  Avestern  highlands  are  a  little  more  than  a 
mile  high,  while  those  of  the  eastern  highland  have  less 
than  half  that  altitude.  In  South  America  the  plateaus  of 
the  Andes  are  about  two  miles  high,  while  those  of  the 
eastern  region  have  less  than  one-third  that  height. 

Economic  Aspect  of  Plateaus. — Plateaus,  especially 
those  of  a  considerable  altitude,  are  generally  unproduc- 
tive. In  some  instances  they  are  so  high  that  but  little 
rain  falls ;  in  others  the  mountain  rims  shut  off  the  moist- 
ure that  is  borne  with  the  winds.  The  rugged  slopes  and 
deep  canons  almost  always  make  commercial  intercourse 


PLAINS,    PLATEAUS,    AND    MOUNTAINS       65 

very  flifficnilt,  and  sometimes  impossible,  except  to  the 
rudest  methods  of  communication.  Because  of  their  un- 
productive character  the  high  phiteaus,  as  a  rule,  are 
sparsely  peopled ;  and  because  of  the  lack  of  intercommu- 
nication the  civilization  of  the  native  peoples  is  not  usu- 
ally of  the  highest  type. 

In  the  lower  plateaus  the  conditions  are  different; 
there  is  generally  a  rainfall  sufficient  for  the  production  of 
food-stuffs,  and  the  land  that  cannot  be  cultivated  is  often 
well  adapted  to  grazing ;  meat,  cattle  products  and  wool 
are  almost  always  associated  with  these  plateaus.  The 
broken  and  dissected  rock  strata  in  many  instances  yield 
minerals  and  metallic  ores  useful  in  the  arts  and  sciences, 
and  the  rugged  character  of  the  surface  often  furnishes  an 
abundance  of  water-power.  In  the  New  England  Plateau 
of  the  United  States  one  may  see  the  results  of  surface 
conditions  in  the  production  of  water-power ;  in  the  Ap- 
palachian Plateaus,  the  results  of  coal  and  iron  produc- 
tion ;  and  in  the  Iberian  Plateau  and  Australia  the  re- 
sults of  grazing  facilities.  The  avooI  from  these  regions  is 
the  finest  in  the  workl. 

Mountains. — Mountains  are  the  most  characteristic 
and  remarkable  features  of  the  landscape.     In  form,  they 


A   SECTION    ACROSS   THK   UINTA    MOUNTAINS 
cV?  single  fold  with  fault.     'After  Powell. 

are  great  ridges  marlccd  by  a  very  rugged  surface.  In 
structure,  they  arc  folds  or  wrinkles  in  the  strata  of  the 
rock  envelope,  or  else  they  are  immense  blocks  of  rock, 
broken  and  [)artly  u))turnod. 


66 


PHYSICAL   GEOGEAPHY 


Mountains  occur  usually  in  sijsfeins,  each  of  which  con- 
sists of  many  ranges,  together  forming  a  distinct  group. 
A  very  extensive  system  is  sometimes  called  a  cordillera. 
Thus,  the  Rocky  and  Andean  Systems  from  the  great 
Cordillera  of  the  AVestern  Continent  Ranges  or  folds  that 
seem  to  be  continuations,  one  of  the  other,  are  said  to  be 
a  chain,  as  the  Sierra  Nevada  and  Cascade  Mountains.  A 
single  fold  may  be  worn  away  so  that  the  broken  strata 
form  ridges  ;  or  the  crest  may  be  weathered  so  unevenly 
that  it  presents  the  appearance  of  a  series  of  notches, 
thereby  forming  a  sierra.     Any  part  of  the  crest  or  summit 

materially  higher 
than  the  rest 
forms  a  peak. '" 
In  most  instances 
the  peak  is  a  high 
crag,  or  a  pinna- 
cle, but  the  name 
is  also  applied  to 
volcanic  cones, 
and  to  elevations 
that  more  prop- 
,    Pocono   Moun- 


•THE  JURA    MOUNTAINS 
«,</  series  of  gentle  folds. 


erly  are    plateaus — as   Broad    Mountain 

tain,  and  Broad  Top,  in  the  Appalachian  system. 

A  mountain  system  is  characterized  generall}^  by  great 
extent,  several  of  the  more  important  exceeding  four  or  five 
thousand  miles  in  length.  Name  three  of  the  greatest 
systems.  A  range,  on  the  contrary,  rarely  exceeds  a  few 
hundred  miles  in  length.  It  gradually  takes  form,  contin- 
ues a  short  distance,  and  then  disappears,  another  to  the 
right  or  the  left  taking  its  place.  The  rolling  hills  that  in 
many  instances  form  the  approach  to  a  system,  are  called 
foot-hills  or,  better,  Piedmont  lands.  The  hollow  or  de- 
pression between  adjacent  ranges  forms  an  intermoutane 


PLAINS,    PLATEAUS,    AND   MOUNTAINS       67 

valJey ;  or  if  Avide  and  apparently  enclosed,  a  2mrk.  A 
valley  that  extends  across  the  range  is  called  a  pass,  a  gap, 
or  a  canon. 

Nature  of  Mountain  Ranges.— In  the  simplest  form, 
as  the  Uinta  Mountains,  there  is  a  single  fold  ;  in  the  Jura 


SECTION    OF   A    DISSECTED    RANGE 
^4  single  fold  is  dissected  into  a  number  of  ridges. 

Mountains  there  are  several  ;  in  other  instances,  as  the 
Alps,  there  has  been  a  mashing  and  crumpling  of  the 
strata,  producing  results  as  irregular  and  complex  as  though 
the  leaves  of  a  book  had  been  pressed  and  crumpled  side- 
ways by  a  great  force. 

The  folding  process  takes  place  slowly — so  slowl}',  in 
fact,  that  no  means  exist  Avhereby  it  can  be  measured  ex- 
cept after  long  intervals  of  time.  This  is  shown  by  the 
conduct  of  certain  rivers  that  flow  across  the  folds.  The 
streams  cut  their  channels  downward  quite  as  fast  as  the 
folds  are  pushed  upward.  So  when  the  fold  has  become  a 
h)fty  range,  it  is  severed  transversely  by  the  stream.  Had 
not  the  ujjthrust  of  the  fold  proceeded  more  slowly  than  the 
downward  cutting  of  the  stream,  the  latter  would  be 
turned  aside ;  in  places  this  seems  to  have  occurred,  but 
even  in  such  cases  tliere  is  always  evidence  that  the  iiplift 
of  the  range  is  very  slow. 


68 


PHYSICAL   GEOGRAPHY 


Excepting  the  core  of  granite,  or  similar  rock  that  iB 
present  in  the  lower  part  of  many  folds,  mountain-ranges 
are  composed  of  strata  of  sedimentary  rock.  Moreover,  it 
is  a  notable  fact  that  the  strata  which  form  them  are  much 
thicker  along  the  folds  than  elsewhere."  Thus  in  the 
Appalachian  Mountains,  the  sediments  composing  the 
folds  are  about  40,000  feet  thick,  while  the  same  strata 
in  the  Mississippi  Valley  are  scarcely  more  than  4,000 
feet  in  thickness. 

Not  all  ranges  present  the  aspects  of  folds,  however. 
The  ridges  in  the  Great  Basin  of  the  United  States  are 
great  blocks  of  sedimentary  rocks  that  have  been  broken 
and  tilted,  and  left  with  edges  partly  upturned.  The 
Sierra  Nevada  and  Cascade  Ranges  are  both  folded  and 
broken,  and  their  abrupt  eastern  slope  is  the  edge  of  an 
immense  block  tilted  toward  the  Pacific. 


BLOCK   MOUNTAINS,    BASIN   REGION 
The  upturned  edges  form  the  ranges. 

The  ideal  system  with  its  parallel  folds  exists,  it  is  true, 
but  it  is  not  common.  In  most  instances  one  finds  a  con- 
fused tangle  of  ridges  and  ranges,  separated  by  intermon- 
tane  valleys  and  crossed  by  gaps  and  passes.  In  not  a  few 
instances  parallel  ranges  are  connected  by  spurs,  as  in  the 


PLAINS,    PLATEAUS,   AND    MOUNTAINS         69 

Sierra  Nevada  aud  Coast  Ranges ;  and  not  infrequently 
several  ranges  seem  to  radiate  from  a  massive  uplift,  as  in 
the  case  of  the  Pamir  highland,  from  which  radiate  the 
great  folds  that  form  the  Himalaya,  Tian  Shan,  Hindu 
Kush,  and  Suliman  Mountains. 

Physiographic  Aspect  of  Mountains.— From  the  mo- 
ment the  process  of  uplift  begins  the  waters  of  the  atmos- 
phere begin  to  level  off  the  folds.  In  general,  the  more 
prominent  a  topographic  feature,  the  more  exposed  Avill  it 
be  to  the  factors  that  produce  erosion.  And  although 
nearly  every  part  of  the  rock  envelope  is  undergoing  denu- 
dation, uplifted  surfaces  generally  sufler  most.  As  the 
process  of  elevation  goes  on,  the  mountain  torrents  carve 
the  slopes  of  the  range  into  a  multitude  of  valleys,  canons, 
ridges,  and  hogbacks. 

Not  only  are  the  flanks  sculptured,  but  the  crests  are 
also  Avorn  away.  The  tops  of  the  folds  being  considerably 
broken  and,  at  the  same  time,  the  most  exposed,  little  by 
little  are  removed,  leaving  the  upturned  edges  in  the  form 
of  long  ridges.  Most  of  the  ranges  of  the  Appalachian 
Mountains  are  ridges  formed  in  this  manner;  there  are 
few  folds,  but  many  ridges. 

The  amount  of  material  removed  from  the  slopes  and 
crests  of  mountains  is  enormous.  The  crests  of  the  Ap- 
jialachian  folds  in  Pennsylvania  are  scarcely  more  than 
two  thousand  feet  high  at  the  present  time  ;  but  if  all  the 
material  that  has  been  removed  could  be  again  heaped 
upon  them,  their  summits  would  be  not  far  from  ten  miles 
high — about  twice  as  high  as  the  loftiest  summits  of  the 
Himala3^an  folds.  Usually  the  slo{)es  and  foot-hills  are 
covered  dee])  with  coarse  rock  waste. ^~ 

Much — probably  most — of  this  material  has  been  re- 
moved by  running  Avater,  but  the  moving  ice  sheet  that  at 
one  time  covered   the  northern  i)art  of  the  Appalachian 


70  PHYSICAL   GEOGRAPHY 

highlands  was  also  a  ])owerful  aoent  in  sculpturing  their 
crests  and  slopes.  Thus,  in  the  North  Atlantic  States  and 
New  York,  where  they  received  the  full  force  of  glacial  ice, 
the  highlands,  in  places,  are  worn  down  almost  to  the  sea- 
level.  In  Pennsylvania,  where  the  wasting  was  less  ef- 
fective, they  are  about  two  thousand  feet  high.  But  in 
the  South  Atlantic  States,  bej'ond  the  limits  of  glacial 
ice,  the  various  ridges  are  more  than  four  thousand  feet  in 
altitude. 

As  a  rule,  therefore,  mountain-ranges  which  show  l)ut  few 
effects  of  weathering  are  comparatively  young.  The  tilted 
blocks  of  strata  that  constitute  the  short  ranges  of  eastern 
Oregon  as  yet  are  scarcely  notched  by  streams,  and  are 
very  slightly  weathered.  The  ridges  of  Nevada  are  much 
more  worn  and  carved,  and  the  liocky  Mountains,  though 
young  as  compared  with  the  Appalachian  folds,  are  very 
much  worn.  The  Laurentian  folds,  the  oldest  in  North 
America,  are  worn  so  greatly  that  their  highest  crests  are 
only  a  few  hundred  feet  above  sea-level. 

The  character  of  the  Aveathering  and  the  landscape 
scenery  as  Avell  depend  partly  on  the  rock  and  partly  on 
the  conditions  of  climate.  In  the  Appalachian  ranges  all 
the  forms  are  rounded,  subdued,  and  graceful.  In  arid 
regions  they  are  apt  to  be  angular.  The  notched  crests  of 
Avestern  ranges  of  the  United  States  and  Mexico  have  sug- 
gested the  name  "  sierra  "  (saw),  the  sharp,  enduring  crags 
of  the  Alps,  "  aiguille  "  {needle),  "  horn,"  and  "  dent "  (tooth). 

Distribution  of  Mountains. — Mountain-ranges  seem  to 
be  incidental  to  highland  regions.  The  great  highlands 
that  border  the  Pacific  and  Indian  Oceans  are  rimmed 
throughout  much  of  their  extent  by  very  lofty  folds.  In 
North  America  the  Eocky  and  Sierra  Nevada  ranges  are 
the  rims  of  a  high  plateau  whose  surface  is  traversed  by 
block  ranees. 


PLAINS,    PLATEAUS,    AND    MOUNTAINS       71 

How  is  this  statement  borne  out  in  the  case  of  South 
America  ?  of  Austraha '?  of  Africa  ?  It  does  not  seem  ap- 
parent, however,  in  the  case  of  Eurasia.  The  great  system 
of  southern  Europe,  extending  from  the  Caspian  Sea  to  the 
Atlantic,  belongs  to  the  principal  highland  of  Eurasia. 
The  Alps  form  the  northern,  and  the  Atlas  Ranges  of 
Africa  the  southern  rim.  What  sea  fills  the  intermon- 
tane  valley  between  them?  A  partly  submerged  chain 
extends  along  the  east  coast  of  Asia  ;  name  the  penin- 
sulas and  principal  island  groups  belonging  to  it.  In 
general  the  great  systems  are  nearest  the  Pacific  and  Ind- 
ian Oceans. 

Valleys.— The  folding  of  strata  into  parallel  ranges 
naturally  forms  valleys  between  them.  The  great  inter- 
montane  valley  of  California,  Oregon,  and  Washington  is 
of  this  character.  Name  the  ranges  between  which  it  is 
situated.  Although  interrupted  by  cross  ranges  it  prac- 
tically extends  from  Puget  Sound  to  the  Gulf  of  Califor- 
nia. The  valley,  a  part  of  which  the  St.  Lawrence  River 
now  occupies,  is  similar  in  structure. 

Most  valleys,  however,  are  the  results  of  stream-cutting 
and  the  general  weathering  that  comes  from  the  action  of 
water.  Shenandoah  Valley,  the  depression  crossing  Vir- 
ginia, is  an  example.  The  rocks  along  the  line  of  the  val- 
ley were  more  easily  worn  away  than  those  to  the  east 
and  the  west,  and  hence  the  valley  resulted  from  their  re- 
moval. The  valley  of  the  lower  Hudson  was  possibly 
foi-med  in  a  similar  manner.'^ 

In  many  instiinces  the;  water  wears  away  the  bioken 
rocks  forming  tlu!  crest  of  a  r:ing(!  more  easil}'  than  it  can 
rtniiove  them  elsewhere.  In  this  way  vaiioc-shapcd  vdl/cf/s 
ura  formed  at  the  sunnnit  of  a  fold.  IMore  commonly, 
liowevei",  tli(!  strcniiis  on  opposite  sides  of  a  range;  wear 
their  clianiK'ls  clc;n-   (o   flui  crest,  partly  Ijrcaking  ihc  lat- 


72 


PHYSICAL   GEOGRAPHY 


ter  down  by  making  deep  notches  across  it.  Many  of  the 
passes  in  the  Sierra  Nevada  and  Rocky  Mountains  are  ex- 
amples ;  ^^  and  so,  too,  are  the  Avater-gaps  of  the  Delaware, 
Susquehanna,  and  Hudson  Rivers.  Water-gaps  are  usually 
at  the  base  level  of  the  range  ;  passes  are  usually  high 
above  it. 


CANOt    VALLEVS,    APPALACHIAN    MOUNTAINS 

In  a  few  instances  the  cross  spurs  that  join  parallel 
ranges  enclose  valleys  of  considerable  extent.  The  Parks 
of  Colorado,  and  the  Pamirs,  both  frequently  classed 
among  plateaus,  are  exam])les.  The  latter  are  situated  in 
a  high  mountain  knot  which,  because  of  its  great  height, 
is  often  called  the  "  Roof  of  the  World." 

Economic  Aspect  of  Mountains. — Notwithstanding 
the  fact  that  mountains  are  sparsely  settled,  and  include  a 
very  large  proportion  of  uncultivable  land,  they  neverthe- 
less exert  a  great  influence  on  life,  its  history,  and  its  in- 
dustries. Ranges  that  face  rain -bearing  winds  may  be  so 
lofty  that  they  intercept  all  tiie  moisture.  How  do  the 
Cascade  and  Sierra  Nevada  ranges  illustrate  this  ?  How 
does  this  affect  the  habitability  of  the  region  west  of  their 
summits  ?  In  various  localities  ranges  at  a  considerable 
distance  from  the  sea  chill  the  Avinds  passing  over  them 
and  condense  the  moisture  that  otherwise  Avould  not  be 
precipitated.  Mountains,  therefore,  are  factors  in  the  dis- 
tribution of  rain. 


PLAINS,    PLATEAUS,   AND   MOUNTAINS       73 

The  broken  folds  of  the  strata  frequently  expose  metals 
and  minerals  that  otherwise  would  not  be  accessible.  Al- 
most all  the  gold  and  silver,  the  mechanism  of  exchange, 
come  from  mountain-ranges  ;  and  so,  also,  does  most  of 
the  copper,  a  metal  necessary  in  the  transmission  of  elec- 
tric power.  Practically  all  the  anthracite  coal  and  much 
of  the  best  iron  ores  are  associated  with  the  rocks  of 
mountain-ranges.  The  latter  are,  therefore,  essential  to 
the  industries  of  mankind. 

Mountains  affect  life  and  its  industries  mainly  because 
they  are  barriers  to  intercommunication.  The  Greek  peo- 
ples of  early  times  found  it  much  easier  to  spread  along 
the  shores  of  the  Mediterranean  and  across  the  vEgean 
Sea  than  to  cross  the  Balkan  Mountains.  For  the  first 
fifty  years  of  our  national  history  there  was  no  transcon- 
tinental intercourse  between  the  Atlantic  and  Pacific 
coasts  of  our  country.  It  was  easier  to  go  sixteen  thou- 
sand miles  around  Cflpe  Horn  than  to  traverse  one  thou- 
sand miles  of  mountainous  surface. 

The  effects  of  intercommunication  n)ay  be  seen  in  the 
case  of  the  Basques,  More  than  two  thousand  years  ago 
they  were  driven  from  the  lo\\lands  of  Spain  and  France 
into  the  almost  inaccessible  valleys  of  the  Pyrenees  Moun- 
tains, During  the  succeeding  years  they  have  been  so  little 
in  contact  with  the  rest  of  the  world  that  their  language 
and  customs  have  been  changed  but  little  in  that  time. 

Because  of  the  differences  of  climate  on  opposite  sides 
of  high  ranges,  the  distribution  of  life-forms  is  greatly  re- 
stricted. The  dense  forests  of  the  Pacific  Coast  can- 
not extend  across  the  Cascade  and  Sierra  Nevada  Kanges, 
because  there  is  not  en(jugh  moisture  to  sup])ort  them. 
On  the  other  hand,  not  many  of  the  plants  of  the  arid  side 
of  the  mountains  can  cross  the  ranges  and  survive  because 
the  conditions  of  climate  and  soil  are  unsuitable. 


PLAINS,    PLATEAUS,    AND   MOUNTAINS       75 

lutermontaue  valleys  are  usually  productive,  and  there- 
fore densely  peopled,  areas.  As  a  rule,  their  fertility  can- 
not be  easily  impaired,  because  fresh  soil  is  brought  to 
them  with  every  flood  season.  Because  of  the  infertile 
region  on  either  side,  the  industries  of  life  are  of  neces- 
sity concentrated  in  the  valleys. 

Passes  have  even  greater  importance  than  valleys.  A 
mountain-range  is  an  obstacle  to  communication,  and  the 
pass  is,  therefore,  the  channel  toward  Avhich  intercourse 
must  be  concentrated.  Eailway  routes  through  mountain- 
ous regions  are  always  surveyed  and  built  through  the 
passes.  Almost  every  railway  to  the  various  commercial 
centres  of  the  Atlantic  seaboard  seeks  a  Avay  through  the 
passes  and  water-gaps  of  the  Appalachian  Mountains. 

To  Mohawk  Gap,  a  pass  that  practically  forms  the 
principal  route  of  traffic  between  the  Great  Lakes  and 
the  Hudson  River,  the  wonderful  development  of  New 
York  City  is  due.  It  is  more  nearly  level  than  any  other 
route  across  the  Appalachian  Mountains,  and  for  this  rea- 
son it  furnishes  a  standard  by  which  freight  rates  between 
Atlantic  seaports  and  the  Mississippi  basin  are  regulated. 

Khyber  Pass,  a  narrow  defile  a  few  miles  east  of  Kabul, 
for  more  than  two  thousand  years  has  been  a  part  of  one 
of  the  great  overland  routes  between  Europe  and  India. 
Indeed,  it  is  the  chief  gateway  to  India;  and  the  truth  of 
the  old  saying,  "  whoso  would  be  master  of  India  must 
first  make  himself  Lord  of  Kabul,"  is  every  day  more  and 
more  emphasized.  It  is  evident,  therefore,  that  inasmuch 
as  mountains  are  a  barrier  between  peoples  upon  their  op- 
posite sides,  all  the  intercourse  and  communication  must 
be  coiK'ciiti-atod  at  tho  passes. 

QUESTIONS  AND  EXERCISES.  Name  and  classify  the  vertical 
forms  in  the  State  in  which  you  live.  On  an  outline  map,  shade  or  oth- 
erwise designate  the  areas  of  highland  and  lowland,  using  such  contours. 


76  PHYSICAL  GEOGRAPHY 

or  lines  of  equal  altitude,  as  may  be  available.  If  possible  use  the  Re- 
lief Map  of  the  United  States  noted  below. 

Make  a  relief  model  in  sand  or  paper  pulp  of  any  locality,  the  topog- 
raphy of  which  you  know— State,  county,  township,  or  other  region 
of  interest. 

What  results  might  occur  were  a  mountain  fold  to  be  formed  across 
the  channel  of  a  river  ? 

Make  a  sketch  restoring  the  plateau  or  mesa  dissected  by  weathering 
processes,  as  shown  on  p.  64. 

Name  some  of  the  benefits  and  the  disadvantages  resulting  from  the 
presence  of  the  Appalachian  Mountains  between  the  industrial  centres 
of  the  Atlantic  Coast  and  the  Mississippi  Valley. 

Explain  why  Fort  Ticonderoga  and  Crown  Point  were  important 
localities  during  the  colonial  wars.  {Consult  any  good  map  of  Lake 
Champlain.) 

On  an  outline  map  of  each  continent,  or  grand  division,  draw  heavy 
lines  representing  the  positions  of  the  principal  mountain-ranges. 

In  what  general  direction  does  the  rock  waste  of  mountains  move  ? — 
Explain  why. 

Give  reasons  why  lowlands  are  more  densely  peopled  than  high- 
lands. 

COLLATERAL   READING   AND   REFERENCE 

McGee. — The  Piedmont  Plateau,  National  Geographic  Mag- 
azine, vii,  261. 

Willis. — Physiography  of  the  United  States,  pp.  169-202. 

HAYE.S. — Physiography  of  the  United  States,  pp.  305-336. 

Powell. — Exploration  of  Grand  Canon,  pp.  181-193. 

United  States  Geological  Survey  Maps,  the  following 
sheets  :  Tooele,  Marion,  Sierraville,  Marysville,  Kaibab,  Farmer- 
^'ille,  Spottsylvania,  Mount  Monadnock,  Mount  Mitchell,  Hum- 
melstown,  and  others. 

NOTES 

'  The  difference  in  the  surface  features  of  these  plains  is  due 
partly  to  altitude  and  partly  to  rainfall.  The  Pampas  resemble 
the  high  plains  east  of  the  Rocky  Mountains.  Both  slope  from  a 
high  to  a  low  level,  and  both  are  covered  with  "  bunch-grass"— 
that  of  the  Pampas  being  a  very  coarse  species  that  grows  to  a 


PLAINS,    PLATEAUS,    AND   MOUNTAINS       7? 

height  of  four  or  five  feet.  The  Llanos  are  watered  by  periodical 
rains  and  are  alternately  a  swamp  anil  a  sun-baked  desert.  The 
Silvas  lie  in  a  region  of  almost  constant  equatorial  rains  ;  hence 
they  are  adapted  to  tropical  forestry.  The  Pampas  and  Llanos 
produce  wild  cattle  and  horses  ;  the  Silvas,  rubber  and  ornamental 
woods. 

*  It  will  be  swept  by  simoon  winds  because  it  will  be  practically 
a  desert,  for  it  is  in  such  regions  only  that  simoon  winds  are 
found.  The  same  is  true  of  the  valley  of  Great  Salt  Lake  :  it 
will  be  a  desert  region  as  soon  as  the  lake  disappears. 

"  Alluvial  plains  are  the  most  productive  lands  in  the  world. 
Because  their  soil  is  constantly  replenished  by  overflows  and 
freshets  they  rarely  wear  out ;  the  nutrient  elements  are  sup- 
plied about  as  fast  as  they  are  exhausted. 

*  The  Atlantic  Coast  Plain  varies  from  a  few  miles  to  more  than 
one  hundred  in  width.  The  more  recently  formed  parts  are  cov- 
ered with  pines  ;  and  a  broken,  narrow  belt  of  pine  forest  extends 
from  Chesapeake  Bay  almost  to  the  Rio  Grande.  To  the  east- 
ward of  the  pine  barrens  is  a  belt  of  sand  flats  and  swamps  of  still 
more  recent  origin. 

"Diluvial  plains  in  places  are  strewn  with  large  bowlders  and 
covered  with  a  "  drift  "  composed  of  sand,  unsorted  gravel,  clay, 
and  bowlders. 

"  A  similar  plain  involves  the  northern  pai"t  of  North  America. 
In  the  New  World,  however,  it  loses  many  of  the  topographic 
features  of  a  plain  and  is,  perhaps  more  accurately,  a  low,  but 
rugged  plateau.  Its  slope,  however,  like  that  of  the  Eurasian 
plain,  is  toward  the  Arctic  Ocean,  and  like  the  latter  plain,  its 
coastal  portion  is  bordered  by  tundras.  Generallj'  considered, 
this  plain  is  a  vast  basin  almost  shutting  the  Arctic  Ocean  from 
the  rest  of  the  sea. 

^  Plains  are  quite  as  subject  to  the  same  weathering  processes 
as  are  mountains  and  plateaus,  but  because  of  their  gentler 
slopes,  the  rate  of  erosion  is  not  so  great  as  in  mountainous 
regions.  The  bluff  lands  along  the  Mississippi  and  some  of  its 
tributaries  are  thus  dissected.  Their  complete  degradation  is  a 
matter  of  time  only.  The  higher  parts  of  the  Atlantic  Coast 
Plain  have  l)een  also  greatly  dissected  by  streams.  In  many  in- 
stances the  stream  valleys  and  flood  plains  cover  an  area  equal 
to  the  inter-streaui    uplands.     In  strong   contrast   are   the  low. 


78  PHYSICAL   GEOGRAPHY 

rt'cently  foriuod  marine  plains  alonj,'  the  southern  coast  of  New 
Jersey,  and  the  still  yonnyer  tule  plains  of  the  Sacramento 
Valley.  In  these  the  rivers  have  hardly  been  able  to  select  their 
channels,  much  less  to  extend  them. 

"  A  high  plateau  sparsely  covered  with  vegetation  is  much  more 
readily  tlissected  by  streams  than  a  grass-covered  surface.  The 
region  through  which  the  middle  course  of  the  Colorado  River 
flows  is  an  example.  Here  the  plateau  has  been  cut  to  a  depth 
ranging  from  three  thousand  to  six  thousand  feet.  The  region  is 
one  of  delicieiit  rainfall,  however.  Extensive  corrasion  is  shown 
along  the  beds  of  the  streams  that  rise  at  a  distance  in  snow- 
clad  mountains.  Only  a  small  part  of  the  plateau  as  yet  has 
been  removed,  and  large  areas  show  but  little  signs  of  dissec- 
tion. In  other  parts,  however,  such  as  the  "Land  of  Standing 
Rocks,"  denudation  has  been  enormous,  and  only  the  towers  of 
harder  rocks  remain.  A  complex  dissection  may  be  seen  in  vari- 
ous parts  of  the  Appalachian  highlands.  Here,  because  of  a 
greater  rainfall,  the  streams  have  formed  a  network  of  canons 
throughout  the  regions. 

'  Such  formations  are  very  common  in  the  lava-covered  regions 
of  the  Sierra  Nevada  and  Cascade  Mountains  ;  they  are  also  found 
in  the  Piedmont  lands  of  western  Texas. 

'"There  are  many  examples  of  isolated  peaks,  or  '"'monad- 
nocks,"  in  those  mountain-ranges  that  have  been  very  greatly 
worn.  Mount  Holyoke  is  one  of  several  examples  in  Massachu- 
setts. It  was  not  thrown  up  in  its  present  form ;  on  the  con- 
trary, it  was  left  when  the  rest  of  the  range,  being  softer,  was 
worn  away.  Mount  Monadnock,  New  Hampshire,  is  a  similar 
example.  I.solated  ridges  or  ranges  are  more  common,  and  ex- 
cellent examples  may  be  found  in  the  Great  Basin. 

"  Not  only  were  the  deposits  that  became  sedimentary  rock 
thicker  before  the  folding  took  place,  but  they  were  made  still 
thicker  by  side  pressure  and  crumpling. 

'*  At  the  mouth  of  every  cafion  there  will  be  found  a  fan-shaped 
pile  of  coar.ser  material  called  talus.  A  pile  of  talus  is  usually 
found  at  the  bottom  of  every  steep,  rocky  cliff. 

'■'A  large  part  of  Rhode  Island  and  Connecticut  constitutes  the 
base  of  an  old  mountain  highland  that  has  been  worn  down  al- 
most to  sea-level. 

"Both  valleys  have  been  modified   by  water,   the  depression 


PLAINS,    PLATEAUS,   AND   MOUNTAINS       79 

having  been  submerged,  partly  filled  with  sediment,  and  re-ele- 
vated. 

'^  It  is  not  unlikely  that  the  process  has  been  more  complex, 
and  that  periods  of  elevation  have  alternated  with  those  of  rest. 
Old  shorelines  and  deposits  of  river  gravel  occur  all  along  the 
lower  river.  The  numerous  clay  banks  seem  also  to  have  been 
deposited  by  slack  water.  The  lower  part  of  this  valley  is  now 
practically^  an  estuary. 

'^  Among  the  famous  passes  are  Argentine,  13,100  feet,  the 
highest  wagon  road  pass  in  the  world;  Marshall  Pass.  10,900 
feet,  one  of  the  highest  railway  passes  in  the  world  ;  Alpine  Pass, 
13,550  feet,  and  Mosquito  Pass,  13,700  feet— all  in  Colorado.  Sim- 
plon,  St.  Bernard,  and  Brenner  are  famous  passes  aci'oss  the  Alps, 
and  for  centuries  they  have  been  highways  of  commerce.  A  rail- 
Avay  pass  across  the  Andes  is  nearly  14,000  feet  above  sea-level. 

In  many  instances  the  pass  is  not  fully  surmounted  ;  instead 
of  building  the  railway  over  the  divide,  it  is  more  economical  to 
construct  a  tunnel  under  it.  Some  of  these  tunnels  are  marvels 
of  engineering  skill.  St.  Gotthard  and  Mont  Cenis  tunnels 
through  the  Alps  ;  Hoosac  tunnel  through  the  range  of  the  same 
name  in  Massachusetts  ;  San  Fernando  tunnel,  in  California  ; 
and  the  tunnel  of  the  Transandine  Railway  are  examples  :  each 
is  one  niile  or  more  in  length.  In  other  cases  the  railway  sur- 
mounts the  range  by  a  series  of  long  and  intricate  loops,  crossing 
and  recrossing  itself  through  tunnels  that  often  are  sharply 
curved.  Near  Caliente,  California,  the  Southern  Pacific  Rail- 
way is  built  in  sinuous  loops  aggregating  about  twenty  miles  in 
order  to  cross  a  tlivide  scarcely  two  miles  from  the  head  of  the 
valley.  The  famous  loops  of  the  Colorado  Midland  over  Hager- 
mans  Pass  is  also  a  well-known  example  of  the  railway  builders' 
skill. 


CHAPTEE  V 


DESTEUCTIVE  MOVEMENTS  OF  THE  ROCK  ENVELOPE : 
VOLCANOES  AND  THEIR  PHENOMENA 

Of  the  various  phenomena  that  attend  changes  in  the 
level  of  the  rock  envelope,  two  of  them,  volcanoes  and 
earthquakes,  are  noteworthy  because  the  results  are  more 


VESUVIUS,  A   TYPICAL   CINDER   CONE 
From  a  model.— ^fter  tj^asmyth. 


or  less  destructive.  In  the  one  case,  great  quantities  of 
molten  matter  are  ejected  from  fissures  or  vents,  covering 
very  large  areas;   in  the  other,  there  is  a  movement  at 

80 


VOLCANOES   AND    THEIR   PHENOMENA       81 

some  part  or  other  of  the  rock  envelope,  so  sudden  that  a 
tremor,  or  even  a  severe  shock,  occurs. 

Volcanoes. — A  channel  or  vent  in  the  rock  envelope 
from  which  great  quantities  of  steam  and  molten  rock  are 
ejected  constitutes  a  volcano}  In  most  instances  a  great 
deal  of  material,  in  the  form  of  clots  of  half-molten  rock, 
fall  about  the  vent  and  build  up  a  conical  pile,  sometimes 
called  a  "volcano,"  but  more  properly,  a  cinder  cone.  At 
the  top  of  the  latter  is  a  cup-shaped  depression  called  the 
crater  or,  if  very  large,  the  caldera.'^ 

Volcanoes  shoAviug  any  display  of  energy  are  said  to  be 
active,  quiescent,  or  inactive,  according  to  the  character  of 
their  energy ;  those  in  which  all  signs  of  activity  seem  to 
have  disappeared  are  said  to  be  extinct.^  In  a  few  in- 
stances the  activity  seems  to  be  continuous.  Thus  the 
caldera  of  Mauna  Loa  nearly  always  contains  lava  in  its 
molten  condition,  and  Stromboli,  "  the  Lighthouse  of  the 
Mediterranean,"  has  been  a  mariner's  beacon  for  more 
tlian  two  thousand  years.  Most  active  volcanoes,  how- 
ever, are  intermittent  in  action,  alternating  their  eruptions 
with  long  periods  of  rest. 

Phenomena  of  Eruption. — In  certain  respects  all  vol- 
canic outbursts  are  similar  ;  that  is,  lava  and  steam  are 
ejected  from  a  subterranean  source,  and  the  matter  ejected 
is  forced  out  of  a  vent  or  channel  in  the  rock  envelope. 
Beyond  this,  however,  the  various  types  of  eruption  have 
but  little  in  common.  In  most  cases  the  eruptions  are 
very  destructive.  Frequently  they  are  preceded  by  earth- 
quakes, though  these  warnings  are  by  no  means  always 
present.  Generally  they  begin  with  explosions  that  rend 
the  top  of  the  cinder  cone  in  fragments.  In  some  instances 
the  plug  of  hardened  lava  that  fdled  the  channel  is  blown 
out,  but  c(uite  likely  a  new  channel  is  formed  at  the  one 
side  or  the  other.^ 


B2 


PH  Y  SIC  A  L   C  EO  G  R  A  PHY 


A  vent  once  made,  the  water  that  had  accumulated  about 
the  cinder  coue,  together  with  inud  and  fragments  of  rock, 
are  hurUnl  upward  ;  an  outrush  of  steam  mingled  with 
mud  and  rock  waste  follows,  and  a  cloud  of  inky  blackness 
quickly  envelopes  the  cone.  The  condensing  steam,  with 
which  sulphureous  vapors  are  sometimes  mingled,  produces 
heavy  rains  ;  and  if  sulphur  gases  are  present,  the  rain 
may  become  so  corrosive  that  vegetation  is  blighted  and 
in  many  instances  the  crops  are  destroyed.^ 

A  flow  of  lava  follows.  At  first  the  lava  is  ejected  with 
almost  explosive  violence,  but  after  awhile  the  How  be- 
comes steady  and 
regular.*^  The 
ejection  of  mate- 
rial takes  place, 
not  only  at  the 
main  vent,  but  at 
the  score  of  new 
formed 


ones 


on 


IDEAL   SECTION   OF  A  VOLCANO 

avliHOr  eruptions  are  taking  place  through  fi^uirc  III  thr  fj.mki    the     flauks    of    tllC 
of  the  cinder  cone,  building  parasitic  cones. 

old.  At  each  vent 
small  monticules,  or  parasitic  cones,  are  quickly  formed, 
and  the  eruption  from  them  does  not  differ  materially  from 
that  at  the  main  vent. 

Volcanoes  such  as  Stromboli  display  but  comparatively 
little  explosive  energy.  From  an  overhanging  crag  of 
this  volcano  the  eruption  may  be  safely  studied.  At  inter- 
vals of  fifteen  or  twenty  minutes  a  gigantic  bubble  begins 
to  form  in  the  caldron  of  seething  lava.  In  a  few  mo- 
ments it  rises  to  the  toD  and  burstinsr,  hurls  a  shower  of 
lava  clots  into  the  air.''  The  eruptions  of  the  Hawaiian 
volcanoes  are  materially  different  from  those  of  the  Strom- 
bolian  or  the  Vesuvian  type.  Instead  of  the  intermittent 
bubbles  of  Stromboli,  or  the  violent  outburst  of  Vesuvius, 


VOLCANOES   AND   THEIR   PHENOMENA       83 

the  lava  rises  in  the  caldera  until  it  overflows  the  lowest 
part  of  the  rini.^  The  flow  of  lava — often  an  enormous 
quantity — continues  for  several  days,  or  perhaps  for  sev- 
eral weeks,  and  then  subsides  as  quietl}-  as  it  began. 

The  fissure  eruptions  that  occurred  in  previous  geologi- 
cal periods  seem  to  have  somewhat  resembled  those  of  the 
Hawaiian  volcanoes.  In  these  eruptions  there  were  ap- 
parently none  of  the  phenomena  that  mark  outbursts  of 
the  Vesuvian  type.  Great  fissures  were  formed,  and 
through    these 

the    lava    Avas  ,, — -"'"'  """---„ 

forced.^  In  some  ,    ^■y-''--^^^:^:^^,:''---^.^         '-v, 

instances  there 
was  an  enormous 
flow  of  lava ;  in 
others  the  lava 
merely  filled  the  ^M 
fissure  and  hard-  a  laccolite 

ened,      leaving     --^4  scclion  thrnush  om-  of  the    Henry    Mountains.       The    dotted 
Unci   indicate  the  strata  removed  by  erosion. 

dykes    oi    v  o  1  - 

canic  rock.  The  plains  of  the  Columbia  are  the  rem- 
nants of  a  flood  of  lava  from  fissures  in  the  Sierra  Nevada 
mountains.  The  Palisades  of  the  Hudson  form  a  dyke 
of  similar  character. 

In  a  few  instances  a  flow  of  lava,  thrust  upward,  has 
raised  the  outer  strata  of  the  rock  envelope  in  much  the 
same  manner  that  a  blister  of  the  skin  is  formed.  No 
extrusion  of  lava  took  place,  and,  as  a  rule,  none  reached 
the  surface.  Irruptions  of  this  kind  form  what  are  com- 
monly known  as  laccolites.  The  Henry  Mountains,  a  de- 
tached group  of  knolls  in  Utah,  are  examples. 

Products  of  Eruption.  —  Excepting  the  very  small 
amount  of  sulphur  gases  emitted,  practically  but  two  sub- 
stances are  ejficted  from  volcanoes — steam  and  lava.     In 


84  PHYSICAL   GEOGRAPHY 

the  eruption  of  Vesuvius  that  occurred  in  1872,  it  is  esti- 
mated that  ninety-eight  per  cent,  of  the  material  ejected 
consisted  of  steam.  From  the  Hawaiian  volcanoes,  how- 
ever, the  matter  thrown  out  consists  almost  wholly  of 
great  quantities  of  lava. 

The  term  lava  includes  every  form  of  molten  rock  of 
volcanic  origin.  Lavas,  therefore,  difier  not  only  in  ap- 
pearance, but  in  chemical  composition  as  well.  In  many 
instances  the  lava  resembles  furnace  slag,  and  has  about 
the  same  composition.  Sometimes  it  is  vesicular,  or 
spongy  ;  pumice-stone,  or  "  volcanic  froth,"  is  so  porous 
that  it  floats  on  water.  Obsidian,  or  "  volcanic  glass,"  an- 
other form,  does  not  differ  materially  from  black  bottle- 
glass.  The  sponge-like  clots  of  lava  that  accumulate  about 
volcanoes  form  scoria;  they  are  suggestive  of  furnace 
"  clinkers." 

A  misunderstanding  of  volcanic  phenomena  has  led  to 
the  adoption  of  certain  names  that  often  give  erroneous 
ideas  of  volcanic  action.  There  are  no  "  flames  "  about 
volcanic  outbursts;  the  so-called  flames  are  merely  the 
reflection  of  the  white-hot  lava  from  the  under  surface  of 
the  dense  clouds  of  steam.^"  "  Smoke  "  is  also  absent, 
except  as  the  clouds  of  dust  and  steam  can  be  thus 
called.  Volcanic  "  ashes  "  are  not  ashes  at  all ;  they  con- 
sist merely  of  finely  divided  lava.  It  is  thought  that  this 
form  of  lavc„  results  from  the  action  of  steam  which,  forced 
through  the  lava  by  intense  pressure,  carries  much  of  it 
along  in  a  fine,  powdery  state. 

Most  lavas  are  readily  decomposed  by  the  action  of  air 
and  moisture,  and  the  Hawaiian  lavas  make  excellent  soil 
in  the  course  of  a  very  few  years.  The  economic  value  of 
lavas,  therefore,  may  be  considerable.  Sulphur,  or  "  brim- 
stone," is  a  common  mineral  in  and  about  the  craters  of 
volcanoes.     It  is  formed  by  the  action  of  certain  sulphur 


VOLCANOES  AND   THEIR   PHENOMENA       85 

gases  that,  on  mixing,  decompose  each  other  antl  deposit 
the  sulphur  in  the  shape  of  crystals. 

Nature  of  Volcanoes. — That  the  cause  of  volcanic  ac- 
tion is  due  indirectly  to  the  gradual  shrinkage  of  the  crust 
of  the  earth  is  admitted  by  most  geographers.  To  what 
extent  the  process  of  contraction  becomes  a  direct  cause, 
however,  is  a  matter  of  uncertainty,  and  one  upon  which 
there  is  a  great  diversity  of  opinion.  It  is  generally  con- 
ceded, also,  that  the  material  ejected  comes,  not  from  an 
assumed  "  liquid  interior "  of  the  earth,  but  is  formed 
at  a  very  moderate  depth  below  the  seat  of  eruption. 


FORMS  OF   ERUPTION 

A,  a  dyke;  B,  E,  subterranean  intrusions;  C,  a  cinder  cone;  D,  a  laccolite;  F,  a  lava  sheet; 
G,  granite  core  of  a  range. 

Various  theories  have  been  advanced  to  account  for  the 
possible  causes  of  eruption,  but  of  these  only  one  or  two 
are  supported  by  positive  evidence.  The  pressure  that 
results  Avhen  the  rock  layers  fit  themselves  about  a  shrink- 
ing interior  is  sufficient  to  heat  the  parts  upon  which  the 
pressure  is  exerted,  far  beyond  the  temperature  of  fusion  ; 
and  if  a  break  or  fracture  takes  place,  the  pressure  being 
relieved  at  that  ])oint,  the  superheated  rock  at  once 
liquefies  and  is  forced  out  of  the  fissure.  The  intrusion 
of  water  upon  molten  matter  undoubtedly  causes  the  ex- 
plosive features  of  the  eruption,  but  it  is  improbable  that 
this  is  the  prime  cause. 


86  PHYSICAL   GEOGRAPHY 

Til  ;i  i"(>\v  iii.st;iiu*es  there  seems  to  l)e  more  or  less  re- 
lation l)('i\v(H>ii  volcanic  vents  situated  at  no  great  dis- 
tance from  one  another.  Thus,  while  Vesuvius  was  so 
long  inactive,  Epomeo  on  the  island  of  Ischia  was  active ; 
but  after  the  eruptions  of  Vesuvius  began  again,  Epomeo 
became  dormant.  A  similar  condition  possibly  obtained 
iu  past  times,  for  the  Phlegrean  Fields,  an  area  south  of 
Vesuvius,  is  honeycombed  with  old  craters  through  which 
eruptions  took  place  at  successive  intervals. 

The  same  phenomenon  is  observed  in  the  case  of  the 
Hawaiian  and  the  Ecuadorean  groups.  Activity  is  us- 
ually confined  to  a  single  caldera,  and  if  this  becomes 
dormant  for  any  length  of  time  the  seat  of  activity  is 
transferred  to  another  vent.  In  the  cases  of  the  Italian 
and  the  Ecuadorean  groups,  the  cessation  of  all  activity  is 
usually  followed  by  a  period  of  frequent  and  destructive 
earthquakes. 

Results  of  Vulcanism. — Notwithstandinsc  their  stu- 
peudous  display  of  energy,  the  physiographic  effects  of 
volcanic  outbursts  are  comparatively  unimportant,  and  as 
a  rule  they  are  confined  to  the  vicinity  of  the  volcano. 
The  most  noticeable  feature  is  the  cone  or  dome  that  pop- 
ularly is  called  a  volcano  or  volcanic  peak.  Each  volcano 
builds  its  own  cone,  and  in  many  instances  the  cones 
have  been  built  along  the  folds  of  mountain-ranges.  In 
several  cases  they  have  been  formed  successively  along  the 
line  of  the  fold  at  no  great  distance  apart. 

The  lava  usually  collects  at  the  vents,  extending  later- 
ally outward,  and  at  the  same  time  building  the  cone  high- 
er and  higher.  The  successive  eruptions  of  the  calderas 
of  Hawaii  have  formed  a  mass  14,000  feet  high  that  covers 
an  area  as  large  as  the  State  of  Connecticut.  Most  of  the 
volcanic  mountains  of  the  Hawaiian  Islands  are  dome- 
shaped  rather  than  conical,  the  shape  resulting  from  the 


VOLCANOES   AND    THEIR    PHENOMENA 


:? 


-^eiy  liquid  conditiou  of  the  lava  and  the  absence  of  ashes 
and  scoria. 

Some  of  the  lava  flows  of  the  Iceland  volcanoes  have 
been  extensive.  Of  the  thirteen  or  more  cinder  cones  in 
the  island  Hekla  and  Skaptar  Jokul  are  the  best  known 
because  of  the  frequency  of  their  eruptions.  In  1783, 
there  occurred  a  flow  of  lava  from  the  latter  that  contin- 
ued for  two  years.  Two  streams  flowed  in  nearly  oppo- 
site directions  from  the  crater,  one  forty,  the  other  fifty 
miles  in  length.  More  than  1,000  square  miles  in  area 
were  covered  by  the  lava.  A  score  of  villages  was  swept 
out  of  existence.     Streams  "were  dammed  bv  the  lava  and 


A    LAVA    FLOOD,   HAWAIIAN    ISLANDS 


tlieir  floods  added  to  the  destruction.  Thousands  of  cat- 
tle wen;  killed,  and  a  large  j)art  of  the  po]>ulation  perished 
in  tlie  famine  that  lesulted  fioin  the  (M-uption. 

The  ashes  sometimes  accomiilisli    inoic   ruin   ilinn  ilint 
which   rt^suUs   from   th(!   lava    How    and    llir  conosive  rain. 


88  PHYSICAL   GEOGRAPHY 

Herculaiiouni  and  Pompeii  were  destroyed  by  the  erup- 
tion of  Vesuvius  a.d.  79.  Pompeii  was  covered  with  loose 
material,  and  much  of  the  city  has  been  excavated  in  re- 
cent years.  Herculaneum  received  a  heavy  fall  of  rain 
in  addition  to  the  ashes,  and  the  latter  were  cemented 
into  a  tolerably  hard  rock. 

In  many  instances  the  ashes  have  been  hurled  to  a  great 
distance,  being  in  part  carried  by  the  wind.  During  the 
eruption  of  Tomboro,  in  Sunda  Strait,  dwellings  forty 
miles  distant  were  crushed  and  large  areas  of  forestry  were 
destroyed.  Similar,  but  more  appalling  effects  resulted 
from  the  eruption  of  Krakatoa,  also  in  Sunda  Strait.  The 
explosions  lasted  for  two  days  and  culminated  with  the 
disappearance  of  half  of  the  island.  Forestrj^  seventy-five 
miles  away  was  crushed  by  the  falling  mud  and  rain,  and 
the  fine  material  covered  the  city  of  Batavia  to  a  depth  of 
several  inches.  Some  of  the  lighter  dust  was  carried  by 
the  wind  to  a  distance  of  more  than  1,000  miles. 

Islands  are  both  formed  and  destroyed  by  the  outbursts 
of  marine  volcanoes.  Off  the  coast  of  Tunis,  near  the 
site  of  Carthage,  a  reef  called  Graham's  Island  was  formed 
during  an  eruption,  and  remained  in  existence  for  several 
years.  It  then  gradually  settled  below  sea-level  and  dis- 
appeared. Several  new  islands  appeared  in  the  group  of 
the  Azores,  during  eruptions,  but  they  gradually  disap- 
peared. A  more  remarkable  case  is  that  of  Santorini,'' 
an  island  in  the  Greek  Archipelago,  which  was  formed  as  a 
result  of  eruptions.     It  is  now  inhabited. 

Fissure  eruptions  are  noted  mainly  for  the  enormous 
flows  of  lava.  From  one  or  more  of  these  fissures  in  the 
Sierra  Nevada  ranges  there  occurred  a  flood  of  lava  that 
covered  more  than  one  hundred  thousand  square  miles. 
Large  areas  of  California,  Oregon,  Washington  and  Idaho 
were  engulfed,  and  in  several  places  the  Columbia  River 


VOLCANOES   AND   THEIR   PHENOMENA        89 

was  pushed  out  of  its  clianuel.  In  mauj  places  small 
cinder  coues  have  been  formed  on  the  surface  of  the 
lava,  each  being  an  eruption  upon  an  eruption.  In  places, 
the  sea  of  lava  is  nearly  four  thousand  feet  deep,  and  the 
average  depth  is  not  far  from  one  thousand  feet. 

Vulcanism  seems  to  be  a  trustworthy  index  of  ]n-ocesses 
going  on  within  the  earth's  crust  which  aiiect  the  level  of  a 
region.  Careful  measurements  have  shown  that,  in  regions 
of  volcanic  activity,  an  elevation  of  the  surface  is  taking 
place.  Thus,  along  much  of  the  Mexican  and  South  Amer- 
ican coast,  where  volcanic  forces  are  active,  upheaval  is 
taking  place.  In  the  South  Pacific  Ocean,  on  the  con- 
trary, where  vulcanism  seems  to  have  recently  ceased, 
there  has  been  a  considerable  subsidence.  It  cannot  be 
said  with  certainty,  however,  that  these  are  matters  of 
cause  and  eftect. 

Distribution  of  Volcanoes. — Volcanoes  are  commonly 
found  along  the  lines  of  the  younger  mountain  folds,  and 
they  are  almost  alwaj'S  near  the  sea.  The  Pacific  Ocean 
is  nearly  girdled  by  chains  of  mountains  that  are  com- 
paratively young,  and  in  these  folds  are  situated  a  majority 
of  the  active  and  dormant  volcanoes  of  the  earth. 

Another  short  chain  extends  along  Java  and  the  re- 
maining Sunda  Islands  to  New  Zealand.  It  contains 
about  one  hundred  active  and  dormant  volcanoes,  and  is 
the  chief  seat  of  volcanic  activity  on  the  earth.  The  Ha- 
waiian group  is  about  the  only  one  situated  in  mid-ocean. 
In  what  direction  does  it  extend  ?  This  chain  is  about  a 
thousand  miles  long.  The  seat  of  activity,  however,  is  con- 
fined mainly  to  the  island  of  Hawaii,  on  which  there  are 
three  calderas — Kea,  Loa,  and  Kilauca. 

A  chain  of  volcanic  islands  cixtends  from  Jan  Mayen 
island  through  Iceland,  the  Azores,  Canary,  and  Cape 
Verd  Islands,  southward  as  far  as  Tristan  da  Cuuha.  An- 


90  PHYSICAL   CtEOCtKAPHY 

other  extends  through  the  West  Indies,  but  it  contains  no 
volcanoes  at  present  active.  Graham  Land,  in  the  Ant- 
arctic Continent,  contains  at  least  two  volcanoes  that 
have  been  active  in  recent  times. 

Among  American  volcanoes  the  Peruvian  and  Ecuado- 
reau  groups  are  famous  for  their  great  height.  Name  three 
of  them.  The  Mexican  group  contains  four  of  interest, 
because  thej  are  so  far  inland.  Find  them ;  in  what 
direction  does  the  line  extend?  Tliej  are  active  or  quies- 
cent at  short  intervals. 

The  North  American  group  contains  a  great  many 
dormant  mid  extinct  cones  ;  but  at  least  four — Shasta,  Ta- 
coma  (or  llainier),  and  Lassen  must  have  been  active  at 
no  greatly  remote  time.  A  small  cone  near  Lassen  Peak 
has  been  in  eniption  within  fifty  or  sixty  years,  and  the 
stumps  of  trees,  many  of  them  in  a  good  state  of  preserva- 
tion, are  still  protruding  through  the  sheet  of  lava. 

Cinder  cones  and  volcanic  "  necks  "  are  abundant  all 
through  the  plateaus  of  the  Western  Highlands.  In  Ari- 
zona there  are  several  hundred.  One  of  the  most  imposing, 
San  Francisco  Peak,  has  been  in  eruption  Avithin  recent 
times.  In  New  Mexico  there  are  also  many  small  cones. 
Almost  all  the  high  peaks  of  the  Cascade  and  Sierra  Ne- 
vada ranges  are  cinder  cones. 

The  Aleutian  group  contains  about  thirty  cones,  quies- 
cent and  active.  One  of  these,  Bogoslov,  north  of  Una- 
laska,  has  been  in  eruption  almost  constantly  since  1880. 
Many  of  the  peaks  of  the  West  Indies  are  cinder  cones, 
but  none  has  been  active  in  recent  times.  The  remains  of 
old  cones  are  abundant  in  the  Appalachian  and  Laurentian 
Mountains,  but  they  seem  to  have  been  extinct  since  early 
geological  times.  One  of  them.  Mount  Eoyal,  has  given 
to  the  city  of  Montreal  its  name. 


VOLCANOES   AND   THEIR   PHENOMENA        91 

QUESTIONS  AND  EXERCISES.— Explain  the  nature  of  the  so- 
called  smoke,  flames,  and  ashes  of  volcanic  eruptions.  Why  are  these 
terms  inapplicable  ? 

Prepare  a  written  description  of  the  geographic  distribution  of  vol- 
canoes, taking  into  consideration  their  position  with  reference  to  moun- 
tain-ranges, proximity  to  the  sea,  latitude,  and  situation  with  reference 
to  continents  and  islands.     Consult  the  map,  p.  92. 

Note  the  features  in  the  diagram,  p.  88,  and  prepare  a  brief  descrip- 
tion of  the  various  ways  in  which  lava  is  extruded. 


COLLATERAL  READING  AND  REFERENCE 

Pli^Hl. — Letters — Book  vi.,  16-vi.  20. 
Shaler. — Aspects  of  the  Earth,  pp.  46-97. 

"  First  Book  of  Geology,  pp.  88-97. 

Le  Coxte.— Elements  of  Geology,  pp.  89-103. 
Redway  axd  Hixman.— Natural  Advanced  Geography,  p.  12. 
United  States   Geologhcal  Survey.— Shasta    and    Lassen 
sheets. 

NOTES 

'  The  channel  or  tube  is  the  essential  part  of  the  volcano,  and 
the  "  mountain  "  or  cinder  cone  is  merely  an  incidental  feature. 
The  latter  is  rarely  absent. 

"^  The  craters  of  the  earth  are  exceedingly  small,  compared  with 
those  of  the  moon.  Terrestrial  craters  are  rarely  more  than  half 
a  mile  in  diameter  ;  lunar  craters,  on  the  contrary,  frequently  ex- 
ceed twenty  or  thirty  miles  in  diameter  ;  Tycho  and  Copernicus, 
are  each  more  than  forty  miles. 

'  As  a  rule,  such  volcanoes  are  rarely  distinguishable,  except  by 
most  careful  investigation.  Usually  the  cone  has  been  almost 
obliterated,  nothing  remaining  except  such  masses  of  lava  as  are 
not  easily  altered  by  the  action  of  moisture  and  atmospheric  ele- 
ments. Mount  Tom,  Massachusetts,  is  an  excellent  example 
of  an  old  volcano. 

*  The  eruption  of  Vesuvius  in  1750  took  place,  not  at  the  former 
crater,  but  a  little  to  one  side.  One  of  the  old  crater  walls  re- 
mained standing,  and  for  many  years  was  called  Monte  Summa, 
During  the  eruption  of  1872  a  large  number  of  vents  was  formed, 


VOLCANOES   AND   THEIR   PHENOMENA       93 


and  the  flanks  of  the  mountain  were  dotted  with  monticules. 

Professor  Palmieri,   who  remained   in  his  observatory  on   the 

mountain    during    the 

entire  period,  said  that 

the  whole  side  of  the 

cone  '  *  seemed  to  sweat 

fire  at  every  pore." 

'  The  sulphur  com- 
pounds combine  with 
the  steam,  making  sul- 
phurous acids,  and  not 
infrequently  the  acid 
dissolved  in  the  rain  is 
strong  enough  to  de- 
stroy vegetation. 

•  It  behaves  exactly 
as  though  it  were  forced 
out  by  gases  under  ex- 
tremely high  pressure, 
the  elasticity  of  the 
medium  that  consti- 
tutes the  power  being 
the  most  noticeable 
feature. 

^  The  phenomena  are 
.simply  those  exhibited 

by  a  viscous  body  in  a  state  of  slow  boiling,  and  are  perfectly 
illustrated  in  the  slow  cooking  of  oatmeal.  It  is  a  significant 
fact  that  when  the  barometer  is  low,  the  level  of  the  lava  is 
higher  than  at  other  times. 

'  There  is  evidence  of  the  presence  of  gases  in  the  Hawaiian 
lavas,  not  under  pressure  and  endeavoring  to  escape,  but  in  a  con- 
dition of  absorption  or  occlusion.  Occasionally,  clots  of  lava  are 
shot  into  the  air,  and  as  soon  as  the  ejected  mass  perceptibly  cools, 
its  absorptive  power  is  lessened,  the  escaping  steam  or  other  vapor 
blowing  the  viscous  lava  into  the  fine,  tenuous  threads  known  as 
"  Pele's  hair."  The  threads  thus  formed  are  so  gossamer-like 
that  they  are  carritid  a  long  distance  by  the  wind. 

°  There  is  a  tendency  to  consider  the  vulcanism  of  past  epochs 
as  crater  eruptions  only.     That  such  eruptions  have  occurred  in 


ALTERATIONS    IN   THE   SHAPE   OF   VESUVIUS 
^'l.'D.  6j,  79  to  1611,  1767,  1822,  1S6S. 


U  PHYSICAL   GEOGRAPHY 

prior  epochs  cannot  be  denied  ;  old  craters  and  the  lava  plugs 
that  filled  them  are  found  in  great  numbers  in  many  parts  of  the 
earth.  Most,  if  not  all,  of  the  great  lava  floods,  however,  came, 
not  from  craters,  but  from  fissures.  No  crater  in  the  world  is  large 
enough  to  have  ejected  a  lava  flood  in  the  manner  in  which  that 
of  the  Oregon  and  Washington  flood  was  spread.  Calderas  like 
those  of  Hawaii  would  have  built  up  a  dome-shaped  mass  of 
ajecta.  The  lava  flood  in  question  was  a  sheet.  It  could  have 
come  from  nothing  but  a  fissure,  and  the  fissure  must  have  been 
many  miles  in  length.  Cinder  cones  and  craters  are  found  here 
and  there  on  the  surface  of  this  vast  sheet.  In  each  case  the  cone 
and  its  crater  represent  a  volcano  that  formed  on  the  lava  flood 
after  the  surface  had  hardened.  This  fact  indicates  that  vulcan- 
ism  occurs  just  as  readily  with  a  supramontane  as  a  sub-moun- 
tain reservoir.  In  many  instances  there  has  been  nothing  more 
than  a  mere  filling  of  the  fissure — em  intrusion  of  lava,  but  no  ex- 
trusion. Not  infrequently  the  vipper  edges  of  the  fissure  walls 
have  been  worn  away,  leaving  the  harder  volcanic  rock  in  the 
form  of  a  ridge  or  dyke.  The  Palisades  of  the  Hudson  are  an  ex- 
ample. The  Devil's  Slide,  in  Weber  Caiion,  Utah,  is  also  an  illus- 
tration. In  this  instance  there  are  two  dykes  about  twenty  feet 
apart,  the  groove  between  them  being  of  softer  rock. 

'"This  may  be  illustrated  by  a  very  familiar  example.  When 
a  train  of  railway  coaches  ]3asses  through  a  long  tunnel,  a  flood 
of  mellow  light  now  and  then  illuminates  the  tunnel  and  the  in- 
terior of  the  coaches.  The  light  comes  from  the  fire-box  of  the 
locomotive.  When  the  furnace  door  is  opened  the  light  of  the 
glowing  coal  is  reflected  from  the  steam  that  fills  the  tunnel. 
Each  globule  of  water  dust  is  a  tiny  mirror,  and  as  a  result  the 
tunnel  is  flooded  with  light.  In  the  case  of  the  volcanic  "  fires  " 
the  light  is  reflected  from  the  under  side  of  the  cloud  of  steam. 

"  This  island,  better  known  as  Thera,  is  a  few  miles  north  of 
Crete.  According  to  one  myth  it  grew  from  a  clod  of  earth  hurled 
from  the  ship  Argo  ;  accoi-ding  to  another  it  was  the  product  of 
submarine  fires.  Both  legends  are  a  testimony  to  its  volcanic 
origin.  The  topography  of  the  island  was  considerably  altered 
by  an  eruption  that  occurred  in  1866.  The  area  covered  by  ashes 
and  .scoria  quickly  became  cultivable,  and  has  since  added  no  lit- 
tle wealtli  to  the  island. 


CHAPTER  VI 

DESTEUCTIVE  MOVEMENTS  OF  THE  EOCK  ENVELOPE  : 
EARTHQUAKES 

Rigid  and  solid  as  tbey  seem,  the  substances  tliat  form 
the  rock  envelope  are  more  or  less  elastic.  This  is  notice- 
able when  an  underground  explosion  ^  occurs,  or  even  Avhen 
a  very  heav}-  Aveight  falls  to  the  ground  ;  the  latter  trem- 
bles for  an  instant,  causing  a  slight  shock. 

Any  instantaneous  disturbance,  therefore,  such  as  a  sub- 
terranean explosion,  the  collapse  of  a  cavernous  space,  or 


THE   I'ROGRESSION   OF   F.ARTHaUAKK   WAVES 

the  sudden  breaking  of  strata,  causes  a  vibration  or  trera- 
Ijliiig  of  the  surrounding  rock.  These  tremt)rs  or  earth- 
quakes may  be  percepti]>le  for  several  seconds,  or  even 
for  so  long  as  a  minute.  The  shock,  moreover,  may  in- 
volve an  area  of  several  thousand  stpiare  miles. 

Nature  of  Earthquakes. — No  matter  how  far   below 

95 


9G  PHYSICAL   GEOGRAPHY 

the  surface  of  tlie  rock  envelope  the  centre  of  the  disturb- 
iince  may  be,  as  soon  as  the  vibrations  reach  the  surface 
they  behave  just  as  do  the  circuhir  waves  that  form  when 
a  stoue  is  thrown  into  still  water.-  In  the  diagram  on 
page  95  the  shock  originates  at  O ;  at  what  place  will  the 
resulting  wave  have  an  up-and-down  motion  ?  These  are 
called  vertical  waves.  As  the  successive  waves  move  out- 
ward, little  by  little  the  vertical  movement  gives  place  to 
one  that  is  both  horizontal  and  progressive,  and  the  latter 
may  be  called  a  horizontally  progressive  wave.  At  Avhat 
part  of  the  diagram  are  the  waves  most  nearly  horizontal  ? 
Where  do  the}^  partake  both  of  the  vertical  and  the  pro- 
gressive character '?  ^ 

The  effects  that  have  been  observed,  however,  indicate 
that  the  tremors  or  vibrations  do  not  always  spread  out  so 
evenly  from  the  centre  of  disturbance  as  is  the  case  with 
the  waves  resulting  Avlien  a  stone  is  thrown  into  water. 
Some  kinds  of  rock  seem  more  elastic  than  others,  and  so 
the  concentric  waves,  instead  of  remaining  circular  in  form, 
become  irregular  in  shape.  If  the  waves  of  water  strike 
an  unyielding  surface,  they  are  rejected,  the  reflected 
wave  often  crossing  the  original  at  oblique  angles.  Rock 
waves,  it  is  thought,  are  similarly  reflected,  and  some- 
times they  produce  effects  that  would  seem  as  though 
there  had  been  a  vorticose,  or  whirling  movement.^ 

Although  the  surface  Avaves  of  earthquakes  bear  a  close 
reseml)lance  to  the  circular  Avaves  formed  by  dropping  a 
stoue  in  water,  it  nnist  be  remembered  that  they  difler 
greatly  in  velocity  and  energy.  The  latter  progress  only 
a  few  yards  a  minute  ;  the  former  have  the  velocity  more 
thai]  doulde  that  of  the  swiftest  projectile  fired  from  a 
modern  gun,  travelling  at  a  rate  that  varies  from  thirty 
to  forty  or  more;  miles  a  minute.^  The  velocity  of  the 
wave   depends   i)artly  on   the   elasticity  of   the   material 


EARTHQUAKES 


97 


through  which  it  travels,  and  partly  ou  the  energy  with 
which  it  is  propagated.  In  hard,  crystalline  rock  it  travels 
rapidly  and  extends  a  great  distance ;  in  sand  and  loosely 
coherent  rock  the  velocity  is  much  slower,  and  the  waves 
quickly     lose     their 


energy. 

In  the  case  of  se- 
vere earthquakes  a 
series  of  shocks  fol- 
low one  upon  another 
with  increasing  in- 
tervals of  time."  The 
first  shocks  are  com- 
monly the  most  vio- 
lent. The  duration 
of  the  shock  is  not 
perceptible  to  the 
senses  for  more  than 
four  or  five  seconds, 
but  careful  measure- 
ments by  the  seismo- 
graph, an  instrument 
for  the  detection  of 
shocks,  show  that  it 
may  last  for  more 
than  a  minute.  In 
many  instances  a 
shock  seems  to  con- 
sist of  a  single  vio- 
lent tlininp.' 

The  focus  of  the  shock  may  vary  from  a  short  distance 
to  several  miles  below  the  surface  of  the  earth.  The 
average  distance  is  not  far  from  six  miles.  The  area 
involved   in    the    earth-wiives   may   be    either   circular   or 


A   ROCK   COLUMN   LIKELY  TO   Bt   OVKRTURNED 
BY  AN  EARTHQUAKE 


The  rock  lias  hrokeii  au-av  from  the  cliff,  splitting  along  a 
naturally  formed  plane.  I^ock  ■waste,  falling  into  the 
ereiiicc,  has  become  saturated  wttli  water,  winch  by  freez- 
ing, has  expanded  and  pushed  the  mass  farther  and 
farther  from  the  cliff. 


98  PHYSICAL   GEOGRAPHY 

elliptical.^  The  diameter  of  the  area  seldom  exceeds  one 
thousand  miles.'' 

Attending  Phenomena.— Earthquakes  are  frequently 
attended  bv  sounds.  Sometimes  the  latter  resemble  low, 
rumbling  thunder ;  more  commonly,  however,  the  noise 
is  like  that  produced  when  a  heavily  loaded  wagon  goes 
rapidly  down  a  gravelled  incline. 

In  the  great  majority  of  earthquakes  the  effects  are 
not  severe  ;  they  rarely  extend  beyond  the  stopping  of 
clock  pendulums,  and  the  swinging  of  chandeliers,  or  the 
breaking  of  delicate  substances.  In  severe  shocks  the 
walls  of  houses  are  wrenched  and  cracked,  and  the  ground 
is  fissured.  In  disastrous  shocks  buildings  are  shattered 
and  the  surface  of  the  earth  is  seamed  with  deep  fis- 
sures and  chasms.  In  several  instances  lakes  ^*'  have  been 
formed  or,  perhaps  drained,  and  stream  channels  changed. 

If  the  centre  of  the  shock  is  in  or  near  the  ocean  it  is 
commonly  followed  by  a  series  of  gigantic  waves,  incor- 
rectly called  "  tidal"  waves.  Following  the  Lisbon  earth- 
quake in  1755,  enormous  Avaves  rolled  in  from  the  sea,  and 
wrecked  whatever  the  earthquake  had  left.'^  The  ocean- 
waves  that  followed  the  earthquake  at  Ai-ica,  Peru,''^  car- 
ried the  United  States  Steamship  Wateree  nearly  seven 
miles  inland,  leaving  her  stranded  in  a  dry  stream  bed. 

Cause  of  Earthquakes.— It  is  generally  believed  that 
earthquakes  are  the  result  of  similar,  but  very  rapid 
movements  of  the  rock  envelope  that  fold  the  strata  into 
mountain -ranges  and  force  molten  lava  from  volcanic 
fissures.  If  the  strata  are  slowly  bent,  no  vibratory  effect 
is  noticeable,  but  if  the  strain  increases  until  a  fracture 
or  a  collapse  takes  place,  the  shock  produces  the  vibra- 
tions that  constitute  the  earthquake. 

When  fissures  are  formed,  usually  one  wall  slips  upon 
the  other,  so  that  the  two  edges  are  no  longer  in  the  same 


EARTHQUAKES 


99 


level.'^  The  resulting  inequality  is  called  a  fault,  and 
wherever  such  faultiugs  are  found,  they  indicate,  if  not 
an  earthquake,  at  least  a  surface  disturbance.  The  ex- 
istence of  such  faults,  therefore,  is  evidence  that  the  outer 
shell  of  the  earth  is  constantly  under  stress "  at  some 
point  or  another,  and  that  the  release  of  the  strain  pro- 
(huH's  the  earthquake. 


AN    hFt-KC.T   OK   THh    KAKHllilAKl      AT    CllAKLLsM.A 
The  crack  when  first  formed  was  about  two  feet  wide.      From  a  photograph. 

Distribution  and  Occurrence  of  Earthquakes.— No 
part  of  the  earth  is  free  from  earthquakes,  and  recent  ob- 
servations have  shown  that,  in  some  part  or  other,  they 
are  of  almost  daily  occurrence.  As  a  rule,  however,  they 
are  so  feeble  that  scarcely  one  in  fifty  is  noticeable,  or 
even  perceptible,  without  the  aid  of  instrumental  measure- 
ments.'^ 

As  in  the  distribution  of  volcanoes,  eartlupiakes  are  of 
more  frequent    occurrence    in    younger   mountain -ranges 


100  PHYSICAL   GEOGRAPHY 

than  in  the  older  ones.  They  are  still  less  frequent  iu 
plains,  unless  the  latter  are  undergoing  a  process  of  uplift 
or  depression.  They  also  accompany  most  volcanic  dis- 
turbances.""' 

The  study  of  several  thousand  earthquakes  shows  that 
shocks  are  a  little  more  frequent  when  the  earth  is  nearest 
the  sun,  and  that  they  are  also  more  prevalent  when  the 
moon  is  nearest  the  earth."  An  explanation  for  this  is 
not  hard  to  find.  Owing  to  the  tendency  to  adjust  itself, 
some  part  or  other  of  the  rock  envelope  is  constantly  under 
an  increasing  stress.  But  when  the  earth  approaches 
either  the  sun  or  the  moon,  the  increased  mutual  attrac- 
tion adds  its  force  to  the  strain ;  the  latter  is  overcome, 
and  a  shock  results. 

QUESTIONS  AND  EXERCISES.— If  you  live  in  the  vicinity  of  a 
body  of  water,  study  the  waves  that  form  when  a  good-sized  stone  is 
tossed  so  that  it  falls  vertically  into  still  water. 

What  is  the  relative  position  of  the  vertical  and  the  horizontally 
progressive  waves  ?  Repeat  the  experiment  until  the  results  obtained 
are  familiar. 

If  possible,  clamp  a  brass  or  metal  plate,  about  a  foot  square,  to  a  firm 
table,  so  that  the  clamp  holds  the  plate  at  its  centre.  Sprinkle  dry 
sand  on  the  plate  and  draw  a  violin  bow  across  the  edge.  From  the 
figures  produced  by  the  sand  note  the  direction  and  character  of  the 
vibrations. 

COLLATERAL  READING  AND  REFERENCE 

Rock  WOOD.— Notes  on  American  Earthquakes. 

Shaler.— Aspects  of  the  Earth,  pp.  1-45. 

Le  Conte.— Elements  of  Geology,  pp.  154-171. 

NOTES 

'Thus,  the  explosion  under  Flood  Rock,  for  the  purpose  of 
clearing  and  widening  Hell  Gate  Channel,  produced  an  earth 
shock  that  differed  in  no  material  principle  from  those  produced 


EARTHQUAKES  101 

by  natural  causes.  The  earth  shock  resulting  from  this  explosion 
was  recorded  at  a  distance  of  nearly  forty  miles  from  Hell  Gate. 
The  velocity  of  the  wave  varied  from  5,000  to  8,000  feet  per 
second  in  the  vicinity  of  the  explosion. 

^  The  vibrations  as  they  form  underground  are  spherical  waves 
and  much  like  those  formed  in  the  air  by  the  discharge  of  a  fire- 
arm or  the  ringing  of  a  bell.  When  the  waves  reach  the  surface 
of  the  rock  envelope  they  spread  out  in  the  form  of  circular 
waves. 

'  Such  waves  have  a  terrific  shattering  force  ;  but  those  in 
which  the  horizontal  and  vertical  components  are  combined  are 
even  more  destructive  :  they  not  only  shatter,  but  they  produce  a 
rocking  motion  as  well.  Vertical  vibrations  may  only  shatter  a 
building  ;  a  "  roller  "  will  not  only  shatter,  but  overthrow  it. 

*  It  has  been  calculated  that  the  amplitude,  or  up-and-down 
motion,  rarely  exceeds  one-quarter  of  an  inch  in  height  ;  and  or- 
dinarily, in  severe  shocks,  it  is  seldom  more  than  one-twentieth 
of  an  inch.  The  horizontal  oscillation  is  scarcely  more  than  half 
an  inch,  and  even  when  it  is  not  more  than  half  as  much,  the 
shock  has  considerable  shattering  power. 

*  During  the  earthquake  at  Riobamba,  Ecuador,  a  vertical 
movement  of  more  than  two  feet  is  said  to  have  been  observed. 
The  statement,  however,  is  not  considered  authentic.  At  all 
events,  the  energy  was  sufficient  to  hurl  heavy  objects  a  hundred 
feet  into  the  air.  The  bodies  of  men  were  thrown  several  hun- 
dred feet  across  the  river. 

'  At  St.  Thomas,  one  of  the  Lesser  Antilles,  the  shocks  of  1808 
aggregated  nearly  three  hundred  in  number.  The  earthquakes 
that  shattered  San  Salvador,  the  capital  of  the  State  of  Salvador, 
la.sted  for  about  ten  days.  The  Charleston  earthquakes  did  not 
cease  for  nearly  a  month,  and  a  hundred  similar  instances  might 
also  be  added.  All  this  accords  Avith  the  well-known  law  that  a 
mass  of  rock  envelope,  in  changing  its  foundations,  cannot  adapt 
itself  to  its  new  position  at  once,  but  does  so  little  by  little. 

'  Many  of  the  California  earthquakes  are  of  this  character. 

*  The  elliptical  form  is  especially  noticeable  in  mountainous 
areas,  and  in  nearly  every  instance  the  major,  or  long  diameter 
of  the  ellipse,  coincides  with  the  trend  of  the  range  or  system. 
The  reason  therefor  is  the  fact  that  the  strata  of  rock  are  more 
elastic  along  than  across  their  masses. 


102  PHYSICAL   GEOGRAPHY 

"In  SL'verul  instances,  however,  the  area  involved  has  far  ex- 
ceeded this.  Thus  the  shock  that  in  1755  destroyed  Lisbon  was 
felt  at  a  distance  of  about  twenty-five  hundred  miles.  The  sea- 
wave  is  propagated  to  a  much  greater  distance. 

'"  The  eartlKpiake  that  destroyed  the  city  of  San  Salvador  broke 
«lo\vn  the  rim  of  a  small  lake  and  drained  it.  The  famous  earth- 
quake of  New  iMadrld,  Missouri,  changed  the  level  of  the  land  to 
such  an  extent  that  a  permanent  swamp  was  formed  in  land  that, 
before  the  shock,  was  high  and  dry.  This  area  has  since  been 
known  as  the  "Sunk  Region."  During  the  severest  shock  the 
current  of  the  Mississippi  is  said  to  have  been  temporarily  re- 
versed ;  that  it  was  greatly  disturbed  is  shown  by  changes  in  its 
channel  occurring  at  that  time.  Reelfoot  Lake,  in  Tennes.see,  was 
considerably  eidarged  at  the  same  time. 

"  Probably  the  most  disastrous  waves  ever  known  to  written 
history,  however,  followed  this  earthquake.  After  the  town  had 
been  felled  by  shocks  so  terrific  that  thirty  thousand  people 
perished,  most  of  the  survivors  took  refuge  on  the  massive  sea- 
wall. Hardly  had  they  reached  it  when  the  water  began  to  re- 
cede, leaving  the  harbor  dry.  Then  an  enormous  wave,  sixty 
feet  high,  rolled  in  and  completed  the  destruction,  and  thirty 
thousand  more  lives  were  swept  out  of  existence  before  the 
Avaves  ceased.  At  Cadiz  the  waves  were  thirty  feet  high,  at 
Madeira  eighteen,  and  along  the  Irish  coast  they  were  four  or 
five  feet  in  height. 

'^  The  sea-wave  resulting  from  this  earthquake  crossed  the 
Pacific  Ocean  and  was  recorded  at  Yokohama,  Japan,  twenty 
hours  afterward.  On  the  American  coast  the  wave  was  observed 
as  far  north  as  Alaska,  and  to  the  westward  as  far  as  Australia. 
The  earthquake  that  in  1854  devastated  a  part  of  Japan  was  fol- 
lowed by  a  destructive  wave.  At  Simoda  the  wave  was  thirty 
feet  high  ;  at  Peel's  Island,  one  thousand  miles  away,  it  was 
fifteen  feet  ;  on  the  California  coast  it  was  from  twelve  to 
eighteen  inches  in  height. 

"  The  destruction  of  Babispe,  a  small  village  in  northern  Mex- 
ico, is  an  excellent  illustration.  This  disturbance,  alleged  to  be 
a  volcanic  eruption,  was  in  reality  nothing  more  than  a  severe 
earthquake  that  levelled  the  buildings  of  the  town.  During 
the  series  of  shocks  a  fissure  was  made,  extending  several  miles 
in  length,  and  when  equilibrium  was  restored,  the  fissure  had  be- 


EARTHQUAKES  103 

come  a  fault — one  side  or  wall  being,  in  places,  from  ten  to  four- 
teen feet  below  the  other. 

'*  At  Monson,  Massachusetts,  the  rock  in  the  granite  quarries 
usually  exhibits  signs  of  heavy  strain.  Professor  Niles  observed 
that  pieces,  before  their  ends  had  been  detached,  were  split  along 
a  horizontal  plane  and  l)ent  upward  at  the  middle.  One  mass, 
measuring  354  x  11  x  3  feet,  increased  an  inch  and  one-half  in 
length  after  it  had  been  detache<l.  These  facts  indicate  the  enor- 
mous pressure  to  which  rocks  may  be  subjected  ;  incidentally 
they  show  that  even  the  hardest  rocks  are  decidedly  elastic. 

'*  An  instrument  for  measuring  any  of  the  elements  of  an 
earthquake  shock  is  called  a  seismometer.;  if  it  merely  records  a 
sh(^ck  it  is  a  seismograph.  The  horizontal  element  of  the  shock 
is  recorded  by  means  of  a  delicate  pendulum  carrying  a  pencil  or 
stylus.  The  jar  sets  the  pendulum  in  vibration,  and  the  pencil 
records  the  direction  of  the  oscillations. 

'*  The  sudden  formation  of  gases  on  their  rapid  motion  from 
one  part  of  the  volcanic  district  to  another,  will  account  for 
earth  shocks  at  such  times. 

"Of  a  total  of  3G4  shocks,  147  occurred  in  the  Atlantic  High- 
lands and  Coast  Plain,  0(5  in  the  Great  Central  Plain,  and  151  in 
the  Pacific  Highlands.  These  figures  have  only  an  approximate 
value,  however,  inasmuch  as  many  of  the  earth  shocks  occurring 
in  the  sparsely  settled  regions  of  the  Pacific  Highlands  escape 
notice  altogether.  Of  66  shocks  recorded  in  Canada,  the  United 
States  and  the  AVest  Indies  during  one  year,  24  were  in  the  At- 
lantic slope  and  the  West  Indies  ;  3  were  in  the  Great  Central 
Plain  ;  and  ;'>!•  in  the  Pacitic  Highlands,  including  Mexico  and 
Central  America. 


CHAPTEE  VII 

THE  WASTING   OF   THE  LAND  :    THE   WORK   OF 
EIVERS 

While  various  forces  are  at  work  wrinkling  and  fokling 
the  strata  of  the  rock  envelope,  other  agents  are  constant- 
1}^  at  work  wearing  away  those  same  folds  and  irregular- 
ities and  wasting  or  degrading  the  surface  of  the  land  to 
its  lowest,  or  base  level. 

The  principal  agent  in  producing  these  effects  is  water, 
in  one  or  another  of  its  different  forms.  Falling  on  the 
land  as  rain  it  removes  fine  and  loose  particles  of  earth. 
It  also  sinks  into  the  pores  of  the  rock,  ]ierhaps  dissolving 
some  of  it  or,  perhaps,  freezing  and  breaking  off  small 
pieces.  This  process  of  degradation  is  called  erosion. 
Gathering  into  swift  torrents,  the  latter  cut  their  channels 
deep  into  the  surface,  producing  the  effects  called  cor- 
rosion. Flowing  against  cliffs  and  banks  or,  perhaps, 
through  underground  channels,  it  saps  the  foundations  of 
masses  of  earth  and  breaks  them  down  by  underiuinimj. 

Gravitation  is  an  aid  in  the  process  of  degradation, 
for  not  only  does  the  water  invariably  flow  downward, 
but  tiie  ddriius,  or  rock  waste  resulting,  is  likewise  mov- 
ing to  lower  levels.  Perhaps,  for  a  time,  it  lodges  in  a 
hollow,  or  basin-shaped  depression,  until  the  l.-ittcr  is 
tilled  ;  then  the  downward  progress  again  begins.     Of  the 

105 


106 


PHYSICAL   GEOGRAPHY 


water  that  falls  from  tlie  clouds  upon  the  land,'  some 
evaporates  and  mingles  with  the  air  ;  a  part  sinks  into 
the  ground,  filling  up  the  underground  channels  and  res- 
ervoirs ;  the  remainder  gathers  into  channels  and  flows 
back  to  the  sea. 

Streams  of  water  flowing  upon  the  land  are  variously 


THI-    BEGINNING   OF  A  LOOP,  CUMBERLAND   RIVER,    KENTUCKY 
The  river  has  built  a  flood  plain  on  the  vest  side  and  is  cutting  into  the  east  hank. 

called  rills,  rivulets,  brooks,  creeks,  and  rivers— the  name 
usually  depending  on  the  size  of  the  stream.  The  largest 
streams  are  rivers.  Almost  every  river  is  made  up  of 
branches  and  tributaries,  and  these,  in  turn,  are  fed  by 
smaller  branches— all  together  comprising  the  river  sys- 
tem. The  area  drained  l)y  the  river  system  is  its  wate7^- 
shed' ov  basin,  and  usually  the  latter  is  surrounded  by  a 


THE   WASTING   OF   THE   LAND  :    RIVERS     107 

well-defined  height  of  land,  the  ridge  or  divide  that  sep- 
arates it  from  adjacent  basins. 

In  some  instances  the  crest  of  a  mountain-range  forms 
a  divide,  but  in  very  many  cases  the  latter  is  an  almost 
imperceptible  rise  only  a  few  feet  high/  Thus,  at  Chi- 
cago, the  divide  between  Lake  Michigan  and  a  tribu- 
tary of  the  Illinois  River  is  only  ten  or  fifteen  feet  high- 
er than  the  level  of  the  lake.  It  must  be  borne  in  mind, 
however,  that  a  high  mountain-range  is  not  necessarily  a 
divide,  for  there  are  many  instances  where  ranges  are 
crossed  by  rivers.  From  any  good  map  find  the  divide 
between  the  Susquehanna  and  Allegheny  Rivers  ;  between 
the  Great  Kanawha  and  Ohio  Rivers.  Compare  the  divides 
with  the  ranges. 

Physiography  of  Rivers. — The  beginnings  of  most 
large  rivers  are  high  in  the  mountains,  where  the  rainfall 
is  heaviest  and  the  greatest  accumulation  of  snow  is  found. 
The  water  that  is  let  loose  from  a  spring  or  from  a 
winter's  snowdrift  trickles  down  the  slope  in  tiny  rills. 
On  their  way  the  rills  unite  into  rivulets  and  brooks  that 
tumble  down  the  mountain  slopes  in  self-made,  pebbled 
gullies. 

Other  streams  join  the  brook  and  swell  its  volume  into 
a  mountain  torrent  that  rushes  down  the  steep  incline, 
cutting  its  channel  into  hard  rock  and  tossing  to  the  one 
side  or  the  other  the  obstacles  in  its  way.  Almost  always 
it  Hows  in  a  deep  canon  or  gorge,  the  cutting  of  Avhich  is 
the  i)rincipal  part  of  its  work.^  When  the  stream  emerges 
from  the  mountain  canon  it  is  burdened  with  rock  waste 
brought  from  the  mountain  side  and,  no  longer  able  to 
carry  all  of  this,  because  of  the  lessened  slope,  it  drojjs 
the  coarser  material,  forming  a  fan-shaped  pile.  Thence- 
forth, because  it  is  no  longer  a  swift  torrent,  it  cannot  re- 
move the  heavier  obstacles,  but  must  flow  around  them. 


108 


PHYSICAL  GEOGEAPHY 


Tlie  lighter  rock  waste,  called  sediment  or  sili,  ^  is  still 
carried  by  the  flood  of  the  river.  Perhaps  a  little  of  it  is 
dropped  here  and  there,  but  the  greater  part  is  borne  to 

the   coast    plain, 


;X~ 


\ 


; 


which  in  many  in- 
stances  is  the 
"made  -land  " 
formed  of  river 
sediments.  After 
reaching  the  latter 
the  silt  is  gradual- 
ly dropped  until 
the  river  reaches 
tide-water.  There, 
about  all  the  rest 
of  the  silt  is  de- 
posited—  either  to 
be  spread  out  in 
the  form  of  a  delta, 
or  to  be  piled  up 
near  the  shore  in 
spits  and  bars. 

It  is  evident, 
therefore,  that  in 
streams  which  are 
degrading  the  land  three  processes  are  usually  going  on, 
namely — corrasion  and  undermining,  transportation,  and 
deposition.  That  is,  from  the  moment  the  water  touches 
the  rock  envelope  it  is  picking  up  particles  of  earth  ;  it  is 
carrying  them  downward;  or  else  it  is  dropping  them. 
^Whichever  it  does,  depends  on  the  current.  Increase  its 
velocity  and  the  water  Avill  pick  up  more  particles  ;  de- 
crease the  velocity  and  it  will  begin  to  drop  them  and 
flow  around  them.     In  the  upper,  or  torrential  part,  most 


LOOPS   AND   CUT-OFFS   OF   THE   LOWER   MIS- 
SISSIPPI 

The  abandoned  channels  are  sometimes  called  "  Bayous  ,' 
they  form  an  intricate  net-work  of  passages. 


THE   WASTING   OF   THE   LAND  :  RIVERS      109 


streams  emphasize  their  right  of  possession  by  cutting 
their  channels  deeper.  In  the  lower  course  the  reverse 
is  apt  to  be  true;  the  stream  clogs  its  channel  with  silt' 
and  is  therefore  compelled  to  make  a  new  one  on  the  one 
side  or  the  other. 

In  the  study  of  such  rivers  as  the  Mississippi  the  rea- 
sons therefor  are  not  hard  to  find.  Because  the  slope  of 
the  plain  through  which  it  flows  de- 
creases, the  velocity  of  the  current  is 
checked,  and  because  of  the  slackening 
current  the  water  is  constantly  di'opping 
its  load  of  silt."  Moreover,  when  the 
latter  has  been  dropped,  the  water  can- 
not pick  it  up  again  unless  the  current 
is  quickened,  and  must  thereafter  flow 
around  it. 

Islands  are  common  in  rivers  carry- 
ing a  considerable  sediment.  The  an- 
choring of  a  snag,  or  any  other  obstacle, 
slackens  the  current  and  causes  the  de- 
position of  silt.  The  latter  increases  in 
amount  until  finally  it  reaches  to  the  sur- 
face. Then  vegetation  gets  root  and  an 
island  results. 

The  river  which  flows  over  a  decreasing  slope  has  a  ten- 
dency, therefore,  to  form  loops  in  its  lower  course,  and  in 
general  the  loops  are  long-lived.  But  when  there  is  a 
succession  of  years  of  increased  volume  of  water,  the  con- 
ditions are  changed.  Because  the  volume  of  water  is 
increased  the  current  is  quickened,  and  the  water  then 
begins  to  pick  up  silt  that  it  had  previously  dropped. 
In  time,  the  neck  of  the  loop  is  cut  away,  and  the  river 
shortens  its  channel  —  sometimes  by  twenty  or  thirty 
miles.'     The  line  of  ituxxts,  or  oxbow  lakes,  along  the  lower 


of  Prairie  du  Chien 


ISLANDS   IN   A   RIVER 


110 


PHYSICAL  GEOGRAPHY 


PALMYRA 


BEND— NOW    PALTVIVRA 
LAKE 


Mississippi  marks  the  old  loops  and  abaudoned  channels 
along  this  river.  It  is  evident  also  that  the  great  amount 
of  silt  removed  when  a  loop  is  destroyed  must  be  carried 

farther  down  stream  and  there 
deposited.  How  would  this 
affect  the  river  so  far  as  the 
formation  of  bars  is  con- 
cerned ?  As  a  matter  of  fact 
the  destruction  of  a  loop  is 
attended  by  changes  in  the 
chanuel  that  are  noticeable 
many  miles  both  above  and 
below  the  loop ;  and  more 
than  a  year  elapsed  after 
Davis  cut-off  had  formed  be- 
fore the  changes  ceased. 
If,  during  a  period  of  sev- 
eral years,  there  is  less  than  the  usual  rainfall,  the  stream 
will  probably  increase  the  amplitude  of  its  loops,  and 
even  make  new  ones.  With  the  coming  of  successive 
years  of  greater  rainfall,  however,  the  volume  of  water  is 
increased,  the  current  is  quickened,  and  the  water  be- 
gins to  pick  up  and  remove  sediment  that  formerl}'  it  had 
been  unable  to  carry. 

Growth  and  Development  of  Rivers. — A  river  and 
its  basin  do  not  constitute  a  fixed,  unchanging  feature  of 
the  land.  On  the  contrary,  every  river  passes  through  the 
various  stages  of  infancy,  maturit}^  and  old  age ;  and  its 
legitimate  work  is  to  carve  away  and  remove  its  basin 
until  every  part  is  worn  away  to  base  level.  The  moment 
any  plain  or  surface — such,  for  instance,  as  the  coast  plain 
of  New  Jersey — is  exposed  to  the  action  of  the  weather,  the 
water  falling  upon  it  begins  to  form  channels  *  and  flow  to 
the  sea.     Such  a  stream  may  be  called  an  infant  river. 


THE   WASTING   OF   THE   LAND  :   RIVERS      ill 

At  first  the  stream  drains  its  water-shed  very  imperfectly. 
It  encounters  many  obstacles;  and  if  the  slope  is  gentle,  it 
finds  not  a  little  difficulty  in 
making  its  channel.    It  is  em- 
baiTassed  by  the  inequalities       the  legitimate  work  of  a 
of  the  surface,  and  because  river 

of      them,     lakes     and     swamps       n  removes  the  rock  waste  from  a  to  B  : 
'  '■  A  B,  the  old  :  a'  b  ,  the  new  profile. 

form  in  the  slight  depressions. 

The  channels  are  apt  to  be  shallow  and  the  divides  between 
the  adjacent  branches  are  neither  permanent  nor  well  de- 
fined. In  consequence,  any  unusual  flood  may  result  in 
the  abandonment  of  an  old  and  the  selection  of  a  new 
channel.  Red  Eiver  of  the  North,  is  an  examj^le  of  an  in- 
fant river. 

As  a  stream  reaches  maturity  its  character  is  changed. 
The  channel  is  deepened  and  cut  nearer   to  base  level. 
The  gullies  of  the  tributary 
streams  become  ravines  and 

many  of  the  latter  are  sculpt-  ^^^ant  stage  of  a  river 
ured  into  broad  valleys.  The  ^"''  ""'""  '"" lZ'^,l"i  '^'  """""' '"  "" 
tributaries  extend  their  chan- 
nels backward  and  not  infrequently  capture  the  waters 
of  other  streams  less  vigorous  {See  Illustration,  p.  US). 
The  mature  stage  is  the  age  of  its  greatest  vigor  and  power. 
It  may  lengthen  itself  at  both  ends ;  it  may  build  a  delta 
at  its  mouth  and  extend  the  latter  seaward,  or  it  may  cut 
its  headwater  channels  back- 
wards. 

The  old  age  begins  when    the  mature  and  senile  stages 

'^  ^  OF   A    RIVER 

the     river     has     cut     away     and         jue  ma,:,  stream  a„d  its  tr.hutar.cs  have 

frnnc^nnrtpd  nil  flip  nv^iilqblp  carved  deep  channels  in  the  plain  A  B :  In 
iranspOlietl    ail     IIIC    avaiiauie     ^,  y  ^,  ,^^    remaining    material    has    been 

material  within  the  reach  of  '"•'''"'  """->'• 

its  various  branches.        Thereafter  it  can  be  revived  only 

by  a  gradual  elevation  of  some  part  of  its  bed,  by  changes  in 


11; 


PHYSICAL   GEOGRAPHY 


its  sl()])e,  or  by  :i  coiisidenible  increase  of  its  volnme.  Just 
as  a  log  moved  against  the  saw  results  in  cutting  the  tim- 
ber, so  a  gradual  uplift  of  the  stream  channel  gives  the 
river  fresh  i)ower  and,  for  a  time,  rejuvenates  it.  An  in- 
crease in  the  volume,  by  quickening  the  current  of  the 
stream,  has  also  a  similar  effect.     If,  as  in  the  case  of  the 


YOUNG  RIVERS 

The  stream  on  the  ri^lil  has  uncovered  lite  ledges  of  hard  rock  shozfn   in  the  margin  and 
falls  have  resulted. 


Uplift  of  Uinta  Mountains  across  Green  River,  the  ele- 
vation is  long-continued,  just  so  long  will  the  river  be 
actively  at  work  at  that  point.  It  can  be  rejuvenated 
along  its  whole  course  by  the  uplift  or  tilting  of  its  water- 
shed in  such  a  manner  as  to  increase  the  current  along  the 
whole  extent.  Uplift  is  nearly  always  followed  by  exten- 
sive stream  corrosion. 


THE    WASTING    OF   THE    LAND:    RIVERS      113 

Flood-Plains.— It  ofteu  liapi^eus  that  a  stream  removes 
more  material  from  its  upper  or  torrential  part  than  it  can 
conveuiently  carry.  The  excess  is  then  spread  over  the 
middle  and  lower  parts  of  the  basin,  forming  the  "  bottom 
lands  "  or  Jlood-pla in. 

The  deposition  of  sediment  is  the  result  of  a  slackening 


MATURE    RIVERS 

The  greater  part  of  the  basin  of  each  has  been  removed.  The  tributary  of  the  cen- 
tral stream  is  carving  its  way  into  the  basin  of  the  river  on  the  right  and  will  eventually 
absorb  the  head  waters  of  the  latter. 

of  the  cuiTent.  In  its  infant  stage  the  river  has  but  lit- 
tle cutting  power  and  usually  can  carry  all  the  material  it 
removes.  When  the  headwater  streams  acquire  greater 
vigor,  however,  they  remove  so  much  rock  waste  that  in 
the  middle  and  lower  courses  the  water  is  overburdened 
with  it,  and  the  process  of  flood  plain -making  begins. 

Along  that  part  of  the  plain  occupied  by  the  stream,  un- 
less the  current  is  increased,  the  deposition  of  sediment  is 
constantly  going  on.  The  river  builds  its  bed  and  banks 
a  little  higher  tlian  the  level  on  either  side,  continuing  the 


lU  rUVHICAL   GEOGRAPHY 

process  until  tlio  (iomiiit^  of  high  water ;  then  it  breaks 
tiirougli  its  self-made  banks  and  selects  a  new  channel  in 
lower  laud.  By  this  process  of  adjustment,  the  river,  in 
turn,  may  occupy  every  part  of  its  flood-plain.  It  there- 
fore follows  that  flood-plains  are  due  to  the  overburdening 
of  the  current  of  the  stream. 

In  its  relation  to  life  and  its  industries,  the  flood-plain  is 
the  most  important  j^art  of  river  physiography.  The  sur- 
face is  always  level,  making  the  region  accessible  to  trans- 
]iortation.  Moreover,  the  rock  waste  is  mixed  with  the  ele- 
ments that  form  the  food  of  plant  life,  and  therefore  the 
flood  plain  has  a  most  fertile  soil.      In  the  Mississippi 


HIG-H     WATER      STAGE. 


^^^ia:.,^^. ,  ,^::^MS^ 


A  FLOOD   PLAIN 
The  dark  shading  represents  the  sediment  deposited  by  floods. 

Valley,  for  instance,  where  the  bluff  lands  produce  twenty 
bushels  of  wheat,  the  bottom  lands  yield  thirty  ;  and  if  an 
acre  of  bluff  soil  yields  one  bale  of  cotton,  the  same  area 
of  bottom  lands  yields  two.  The  greater  part  of  the  Chile 
of  geography  is  a  simoom-swept  desert  with  scarcely  a  sign 
of  life  excepting  that  which  pertains  to  the  mines  and  the 
mountain  valleys.  The  real  Chile  is  found  in  the  densely- 
peopled  flood  plains  of  the  Andine  streams.  In  these  short 
valleys  are  concentrated  nearly  all  the  activities  that  go 
to  make  a  great  state. 

Neither  do  we  find  the  Egypt  of  history  in  the  broad 
stretch  of  land  lying  between  the  Red  Sea  and  the  Libyan 
Desert.  On  the  contrary,  the  four  thousand  years  of  his- 
tory that  has  given  to  the  world  so   much  that  goes  to 


THE  WASTING   OF   THE   LAND:   RIVERS      115 

make  up  modern  civilizatiou,  belongs  to  the  flood  plain 
of  the  Nile.  What  has  been  the  efiect  of  the  Mesopo- 
tamia on  the  history  of  the  East? 

Terraces. — After  a  river  has  cleared  away  all  the  rock- 
waste  and  silt  it  can  reach  at  the  headwaters,  the  stream 
may  then  turn  its  cutting  power  against  its  flood-plain. 
Instead  of  depositing  sediment,  the  water  begins  to  re- 
move it.  So  it  forms  a  deeper  channel,  along  the  sides  of 
which  a  new  and  lower  flood-plain  is  built.  The  new  flood 
l^lain  with  the  remnant  of  the  old  one  form  terraces.  Of 
these  there  may  be  three  or  even'four.  Ultimately,  how- 
ever, nearly  or  quite  all  the  flood-plain  is  removed. 


..<,^^^y-^^<y.^  <  /„ -  .^  ^^,  ,y  ,  /m/.'//m//,/   //„//. „///m./,j'..//m/////„  ,./»///. . .  '■  ,    ...mm 


TERRACES    IN    A    Fl.OOD-PI.AIN 
Each  marks  a  stage  of  down-culltng.     The  darker  shading  shows  the  otd  bed  of  the  river. 

It  is  evident,  therefore,  that  flood-plains  and  terraces  are 
merely  incidents  in  the  history  of  a  river.  Perhaps  most 
of  the  rivers  of  the  United  States  are  in  the  flood-plain 
stage  of  their  existence.  Many  of  the  streams  of  the  north- 
eastern part  are  in  the  terrace  stage  and  are  approaching 
the  period  of  old  age. 

Deltas  and  Estuaries. — Salt  water  has  a  very  remark- 
able effVict  in  clearing  muddy,  fresh  water,  and  the  mo- 
ment the  two  mix  the  remaining  silt  held  in  suspension 
is  quickly  deposited.  It  follows,  therefore,  that,  unless 
the    sediment    is    swept    away    by  currents   and    tides,   a 


iin 


PHYSICAL   GEOGRAPHY 


cousidorablo  ixccumiilatiou  will  form  at  the  moTith  of  the 
river. 

The  accompanying  figure,  the  delta  of  the  Mississippi 
River,  shows  one  of  the  most  interesting  types  of  delta  for- 
mation. It  is  evident,  in  this  case  at  least,  that  the  banks 
of  the  delta  are  self-made,  and  that  they  have  been  formed 
because  the  current  has  been  checked  more  effectually  at 


'i.Orand^T'. 

Paaa  '  JETTIES 

South  Pass 


A   DELTA   MOUTH:    THE   DELTA   OF  THE   MISSISSIPPI   RIVER 


the  edges  than  in  mid-stream.  It  is  also  evident  that  since 
the  lower  Mississippi  has  occupied  its  present  channel, 
the  river  has  built  its  lower  part  nearly  one  hundred  miles 
into  the  Gulf  of  Mexico. 

The  deltas  of  the  Volga,  and  Ganges- Brahmaputra  are 
considerably  more  intricate  than  that  of  the  Mississippi. 
They  are  likewise   older,  and  therefore  more   compactly 


THE    WASTING  OF   THE    LAND  :   RIVERS      117 


filled  Avitli  sediment.  The  delta  of  the  Ganges-Brahmapii- 
tra  is  perhaps  the  most  extensive  known.  Its  frontage  on 
the  Indian  Ocean  is  about  two  hundred  miles,  and  its  area 
about  twice  that  of  the  State  of  Texas.  Much  of  the  land 
consists  of  shifting  mud-flats,  and  the  whole  region  is 
subject  to  destructive  inundations. 

The  delta  of  the  Adige-Po  has  developed  in  a  manner 
not  unlike  that  of  the  Ganges.  Probably  no  other  river  of 
its  size  in  the  world  brings  down  more  sediment  than  the 
Po.  As  a  result  its  delta  is  filling  and  extending  very 
rapidly — so  rapidl}',  in  fact,  that  the  town  of  Adria  (Had- 
ria),  in  Julius  Caesar's  time  a  seaport,  is  now  more  than 
twent}'  miles  inland.  Ostia,  in 
early  historic  times,  at  the 
mouth  of  the  Tiber,  is  now 
about  seven  miles  inland. 

With  respect  to  economic 
value,  delta  lands  surpass  al- 
most all  others  in  the  possibil- 
ities of  productivity.  The  soil 
is  exceedingly  rich,  and,  because 
of  the  constant  additions  from 
the  river,  it  is  enriched  as  fast 
as  its  nutritive  elements  are 
taken  up  by  vegetation.  The 
Nile  delta  has  long  been  known 
as  the  granary  of  Egypt — the 
Sunderbunds  of  the  Ganges- 
Brahmaputra  are  foremost  Chesapeake  bay:  an  estuary 
among  the  great  rice-producing 
fields  of  the  world. 

An   inspection    of   any   good 
map  will  disclose  the  fact  that  while  some  rivers  reach  the 
sea,  each   through  a  delta,  others  equally  powerful  with 


OR  SUBMERGED  RIVER  MOUTH 

A  part  of  a   comparatively   level  plain 
has  subsided  below  sea  level. 


18 


riLYSlCAL   GEOGRAPHY 


respect  to  current,  flow  into  estuaries.  The  Mississippi 
and  the  Dehiware  are  contrasting  examples.  In  the 
former  case  the  river  has  a  tendency  to  block  its  mouth 
with  silt ;  in  the  latter,  a  downward  movement,  or  sink- 
ing of  the  coast  has  practically  drowned  the  mouth  of 
the  river.  Moreover,  the  action  of  the  tide  is  usually 
strong  enough  to  keep  the  channel  clear  of  silt  bet\\'een 


A   FJORD   MOUTH   OF  A   RIVER 
lis  situation  adapts  it  for  the  centre  of  commerce  of  a  newly-settled  region. 

bars.  So,  between  the  scouring  action  of  the  tide  and 
the  sinking  of  the  valley  there  is  not  only  a  broad,  but 
a  deep  area  of  water  in  most  estuaries.  If  the  mouth  of 
the  river  is  in  a  coast  plain,  the  estuary  usually  takes  the 
form  similar  to  that  of  Delaware  River.  Along  a  rugged 
coast  with  an  abrupt  slope,  however,  the  estuaries  more 
commonly  are  like  the  indentations  of  the  Maine  coast. 
They  are  also  numerous  along  the  coast  of  Norway,  where 
they  are  caXled.  fjords. 


THE   Wx\STmCT   OF   THE   LAND  :   RIVERS      119 

In  rivers  that  flow  mto  estuaries,  the  sediment  is  de- 
posited in  the  form  ot  bars.  In  most  instances  two  bars 
are  formed,  one  at  the  mouth,  the  other  at  the  head  of  the 
estuary.  The  reason  for  this  double  deposition  of  sediment 
may  be  found  in  the  action  of  the  tides.  Bars  are  formed 
in  comparatively  still  water,  so,  when  the  tide  is  slack  at 
flood,  the  deposition  takes  place  at  the  head  of  the  estuary 
where  the  salt  and  the  fresh  water  meet ;  when  the  tide  is 
ebb,  the  two  waters  meet  at  the  mouth  of  the  estuary  and 
the  deposition  of  sediment  takes  place  at  the  lower  end. 

It  is  evident  that  the  estiiary  favors  commerce  and  navi- 
gation while  the  delta  on  the  whole  is  a  hindrance.  In 
the  case  of  the  Mississippi,  the  navigable  channel  of  the 
delta  has  been  kept  open  at  an  enormous  expense.  Of  the 
great  seaports  that  are  centres  of  commerce,  by  far  the 
greater  number  are  on  the  shores  of  estuaries. 

Cascades  and  Rapids. — In  flowing  to  lower  levels,  if 
the  slope  is  abrupt,  the  water  descends  in  a  series  of 
rapids  in  the  form  of  reaches  more  or  less  terraced.  The 
streams  of  the  New  England  Plateau,  and  to  a  greater  de- 
gree the  torrents  of  mountainous  regions  are  illustrations. 
In  some  instances,  however,  the  stream  plunges  over  a 
vertical  embankment  in  the  form  of  a  cascade  or  fall. 
Of  these,  Niagara  Falls,  Spokane  Falls,  and  those  of  the 
Zambesi  River  are  illustrations.  In  some  instances  moun- 
tain streams  make  tremendous  leaps.  In  the  Yosemite 
Valley,  Merced  Eiver  in  three  plunges  falls  2,600  feet ;  and 
Bridal  Veil  fall,  with  a  sheer  pitch  of  1,500  feet,  reaches  the 
lower  level  in  the  form  of  fine  water  dust.  TheStaubbach 
("brook  dust")  of  the  Alps  is  a  similar  cascade,  having  a 
fall  of  900  feet.  The  Cascade  Range  of  the  United  States 
and  the  Lauterbrunnen  ("  nothing  but  fountains  ")  of  Al- 
pine Europe  are  names  that  suggest  the  character  of  these 
regions. 


130 


PHYSICAL   GEOGRAPHY 


In  some  instances  the  stream  has  had  little  to  do  with 
making  the  cliffs  over  which  it  falls  ;  in  other  cases,  how- 
ever, the  river  itself  has  made  the  falls.  If  a  stream  flows 
over  the  edge  of  a  hard  layer  that  rests  on  a  softer  material, 
the  latter  will  be  more  quickly  removed ;  moreover,  as  the 
softer  layer  is  Avorn  away,  the  fall  becomes  greater  and  the 
water  acquires  an  increased  cutting  power  because  it  has  a 
constantly  increasing  distance  to  fall.     Finally  the  stream 


SECTION   OF  A   WATERFALL 
The    stratum  at  the  top  of  the  fall  is  harder  and  more  resistant  than  the  strata  below. 

cuts  away  so  much  material  at  the  lower  level  that  a  cata- 
ract results. 

In  this  manner  the  falls  of  Niagara  Eiver  were  formed. 
There  is  an  upper  layer  of  hard  limestone  surmounting  a 
deep  layer  of  softer  rock.  The  upper  layer  offers  consid- 
erable resistance  to  the  water  ;  the  lower  layer  is  easily  cut 
away.  Hence  the  falls  are  increasing  rather  than  decreas- 
ing in  height.     The  upper  layer,  however,  is  worn  not  a 


THE  T\^ASTING   OF   THE   LAND:   EIVERS      121 

little,  and  the  falls  are  receding  up  stream  at  the  rate  of 
nearly  two  and  oue-lialf  feet  a  year.^" 

There  are  many  cataracts,  however,  that  are  the  result 
of  accident.  Thus,  a  flow  of  lava  across  Columbia  River 
dammed  the  channel  and  formed  the  well-known  cascades, 
A  similar  lava  flood  at  the  same  time  obstructed  its  chief 
tributar}',  the  Willamette  River,  forming  the  cataract  at 
Oregon  City. 

Falls  and  rapids  frequently  occur  in  the  terrace  stage 
of  rivers,  although  they  may  be  developed  in  early  matu- 
rity. They  are  rarely  found  in  the  flood-plain  age,  because 
the  Hood-plain  buries  all  inequalities.  After  the  stream 
has  carved  away  its  tiood-plain,  it  may  uncover  and  develop 
its  former  rapids  and  cascades. 

Migration  of  Divides. — As  a  rule,  every  stream  works 
most  actively  in  the  upper  or  mountain  part  where  its  cur- 
rent is  swiftest.  As  the  various  headwater  streams  deep- 
en their  gullies  they  frequently  extend  them  to  a  consider- 
able distance  backward;  and  a  very  vig(jrous  stream  may 
even  cut  its  channel  backward  across  a  ridge  or  height  of 
land.  The  latter  then  ceases  to  be  the  water-parting  ;  the 
divide  therefore  "  migrates "  or  recedes  from  its  former 
position. 

In  cutting  its  channel  backward  across  a  ridge  or  height 
:)f  land  a  stream  sometimes  captures  and  diverts  a  part  of 
the  feebler  stream  flowing  on  the  opposite  side  of  the  chan- 
nel (S'-''  iUusfrafion,  p.  113).  Many  of  the  "  wind  gaps  "  of 
the  Appalachian  region  are  the  results  of  this  sort  of  river 
j)iracy.  They  are  abandoned  stream  channels  —  aban- 
doned Ijecause  the  former  occupant  of  each  has  been  capt- 
ured further  up  the  valle}'  by  a  more  vigorous  stream  that 
has  crossed  the  height  of  laud  to  get  it.  The  Vistula 
River  has  probably  obt.-iined  several  of  its  headwater 
streams  by  the  robbery   of  a  neiglil)or,  and   at  least  one 


123  PHYSICAL   GEOGRAPHY 

stream  in  North  western  Ohio  and  several  in  Pennsylvania 
seem  to  have  suffered  in  a  similar  way. 

Unusual  Adjustments. — In  selecting  a  new  channel 
or  in  adapting  itself  to  the  changing  conditions  of  an  old 
one  a  river  is  said  to  adjust  itself.  There  are  several 
causes  which  may  compel  a  stream  to  change  its  course. 
It  may  clog  its  channel,  or  the  latter  may  be  obstructed 
by  accident.  Thus,  by  long-continued  silting,  the  Hoang 
River,  "  China's  sorrow,"  built  its  channel  higher  than 
the  divide,  near  the  top  of  which  it  flowed.  In  1852,  dur- 
ing a  season  of  high  floods,  the  river  broke  through  its 
banks.  Before  that  time  it  had  flowed  southeasterly  from 


TUOLUMNE   RIVER,    CALlhORNlA 

The  ol<i  stream  cltuiiini  i\  uiiilcr  the  lava  cap  which  fonm    Tabic    Mountain  :    the  present 
chaiiiiels  are  at  the  base  of  the  mesa. 

Kaifong  into  the  delta  of  the  Yangtze  ;  after  the  break  its 
course  lay  in  a  northeasterly  direction  and  the  river  now 
flows  into  the  Gulf  of  Pechili. 

The  flood  of  lava  that  formed  the  ])lains  of  the  Colum- 
bia buried  beneath  it  a  long  stretch  of  the  river  basin,  and 
the  river  made  a  new  channel  around  the  lava  flood. ^^ 
Tuolumne  Ptiver,  California,  was  similarly  buried,  but 
finally  succeeded  in  making  another  channel  through  the 
obstruction.  It  is  not  unlikely  that  Saskatchewan  Eiver 
was  cut  in  two  by  the  rise  of  a  height  of  land  across  its 
course,  the  water  being  ponded  in  Lake  Winnipeg  and 
then  overflowing  into  Hudson  Bay. 

Indirectly,  man  is  responsible  for  the  abnormal  conduct 


THE   WASTING    OF   THE   LAND  :   RIVERS      123 

of  certain  rivers,  and  the  cause  thereof  is  the  cultivation 
of  the  hind.  In  order  to  make  his  bnd  productive  the 
farmer  must  not  only  clear  it  of  growing  timber  and  de- 
stroy the  smaller  vegetation,  but  he  must  also,  in  many 
instances,  provide  a  system  of  rapid  drainage.  Because 
forestry,  shrubbery,  and  sod  all  serve  to  retain  water  in 
the  soil  they  therefore  prevent  rapid  drainage.  The  re- 
moval of  vegetation,  on  the  contrary,  has  exactly  the 
opposite  effect.  The  rainfall  is  rapidly  collected  by  the 
tributaries,  and  as  quickly  poured  into  the  main  stream. 
As  a  result,  high  and  quickly-forming  floods  occur. 

The  Ohio  and  the  Susquehanna,  especially  in  late  years, 
have  sufitered  much  from  disastrous  floods,  and  these  are 
mainly  the  result  of  deforesting  their  basins.  Wooded  and 
grass-covered  slopes  are  slowly  drained  ;  denuded  slopes 
favor  rapid  accumulation  of  drainage  waters. 

Geographical  Distribution  of  Rivers. —  Rivers  are 
the  offspring  of  rainfall  and,  as  a  rule,  regions  of  great 
rainfall  are  regions  in  which  rivers  are  largest  and  most 
numerous.  This  is  shown  in  the  case  of  the  Amazon  and 
the  Kongo,  Both  rivers  are  situated  within  the  belt  of 
almost  constant  rains.  Each  has  a  large  number  of  pow^- 
erful  triljutaries,  and  each  discharges  an  enormous  quan- 
tity of  water. 

A  river  cannot  develop  great  length  and  size  unless  the 
water-shed  that  it  drains  has  also  a  great  superficial  extent, 
Wlien  Coluudjus  entered  the  mouth  of  the  Orinoco,  he  at 
once  declared  the  country  southward  to  be  a  continent, 
for  the  reason  that  so  large  a  river  could  not  exist  on  a 
small  Ijody  of  land. 

There  is  no  a])parent  law  governing  the  distribution  of 
rivers  except  the  ])()sition  of  slopes  and  the  amount  of 
rainfall.  The  largest  rivers  are  not  in  tin;  largest  conti- 
nents, nor  are  the  longest  streams  in  regions  of  greatest 


134  PHYSICAL   GEOGRAPHY 

raiuMl.  The  Atlantic  receives  the  waters  of  more  lai'ge 
streams  than  any  other  ocean ;  tlie  Arctic  Ocean  is  the 
next  in  order.  The  reason  therefor  is  the  fact  that  tlie 
largest  plains  slope  toward  the  one  or  the  other  of  these 
two  oceans. 

The  great  jilains  and  slopes  of  the  Western  Continent 
receive  the  full  benefit  of  moisture-laden  winds ;  and  the 
rivers,  as  a  rule,  reach  a  higher  state  of  development  than 
those  of  the  Eastern  Continent.  The  Mississippi  and  the 
Amazon  drain  each  a  water-shed  half  as  large  as  Europe. 
The  Mackenzie,  La  Plata,  Yukon,  Columbia,  and  Colo- 
rado al)out  equal  in  size  the  great  master  streams  of  the 
Old  World. 

The  broadest  part  of  South  America  is  crossed  b}^  an 
almost  constant  rain  belt,  and  therefore  is  in  the  region 
of  heaviest  rains.  The  ocean  winds  traverse  a  sweep  of 
about  2,500  miles  before  they  are  arrested  by  the  Andes 
Mountains ;  and  because  precipitation  covers  such  an 
enormous  area,  there  necessarily  results  a  stream  of  vast 
proportions.  As  a  matter  of  fact  the  Amazon  discharges 
a  greater  volume  of  water  than  any  other  known  river. 

The  chief  plain  of  the  Old  World  faces  the  Arctic 
Ocean.  It  is  the  largest  plain  in  the  world,  and  is  drained 
by  large  rivers.  None  of  them. equals  the  Amazon  nor  the 
Mississippi-Missouri,  however,  for  the  reason  that  they 
are  situated  in  a  region  of  very  moderate  rainfall. 

The  southern  part  of  Europe  does  not  extend  into  the 
region  of  tropical  rains ;  hence  the  absence  of  large  streams 
on  the  southern  slope.  The  southern  part  of  Asia  is  un- 
der the  tropical  rainbelt,  but  the  drainage  slope  is  com- 
paratively short,  and  but  few  large  streams  have  formed. 
Thus  it  may  be  seen  that  the  large  plain  of  Eurasia  is  un- 
favorably situated  for  large  rivers,  while,  on  the  other 
hand,  the  favorably  situated  areas  are  too  small  for  the 


THE    WASTING   OF   THE   LAND  :   RIVERS      125 

development  of  great  streams.  The  great  number  of 
smaller  rivers,  moreover,  compensates  for  the  absence  of 
such  rivers  as  the  Amazon. 

Africa  possesses  several  large  rivers,  two  of  which,  the 
Kongo  and  the  Nile,  are  of  considerable  interest.  The 
Kongo,  like  the  Amazon,  is  an  equatorial  stream,  and 
the  behavior  of  the  two  is  almost  identical.  The  Kongo 
is  smaller  only  because  its  basin  is  smaller.  The  Nile 
is  remarkable  for  its  annual  overflows,  and  from  the  fact 
that,  in  the  lower  1,200  miles  of  its  course  it  receives  not 
a  single  tributar}'. 

Australia  possesses  but  few  permanent  streams,  and 
these  are  of  small  size.  This  continent  is  unfortunately 
situated.  It  is  under  the  Calms  of  Capricorn,  and  it  con- 
tains no  high  mountain  range.  The  Murray-Darling  is 
the  only  river  of  importance.  In  the  summer  season 
most  of  the  streams  disappear  altogether,  or  else  form  a 
succession  of  shallow  pools. 

Continental  Rivers. — There  are  several  large  areas 
that  have  no  drainage  to  the  sea,  and  the  rivers  are  there- 
fore called  continental  rivers.  Where  is  the  continental 
region  of  Eurasia  ?  It  is  drained  by  a  multitude  of  riv- 
ers ;  name  the  four  largest.  In  Africa  the  only  large  con- 
tinental rivers  are  those  flowing  into  Lake  Chad.  There 
are  many  continental  rivers  in  Australia.  Practically  all 
of  them  are  dry  in  summer  and  some  are  filled  only  when 
an  occasional  cloud-burst  pours  a  flood  of  water  into  their 
channels. 

The  Humboldt,  Carson,  and  Jordan  are  the  principal 
continental  streams  of  North  America.  Describe  their  sit- 
uation honi  any  convenient  map.  What  do  they  indicate 
with  reference  to  rainfall '?  AVhat  would  be  the  probable 
eff'ect  on  these  rivers  if  the  Sierra  Nevada  ranges  were  no 
higher   than    the    Appalachian    Mountains  ?      In   South 


126  PHYSICAL   GEOGRAPHY 

America  the  Desaguadero,  the  outlet  of  Lake  Titicaca,  is 
the  piincipal  continental  stream,  although  one  or  two  of 
the  larger  rivers  in  Ai'gentiua  are  occasionally  cut  off 
from  the  sea. 

Economic  Importance  of  Rivers. — Eivers  are  the  most 
important  highways  of  commerce  and,  in  many  ways,  are 
the  lines  along  which  civilization  and  settlement  penetrate 
to  the  interior  of  a  country.  Even  at  the  present  time 
merchandise  can  be  carried  by  means  of  river  navigation 
for  less  than  the  cost  of  transporting  it  in  any  other  way. 
Most  of  the  great  migrations  of  peoples  have  followed  the 
lines  of  rivers,  and  in  mountainous  regions  the  cultivated 
areas  are  confined  mainly  to  river  valleys.  Outside  the 
Great  Central  Plain  of  the  LTnited  States  most  of  the  rail- 
ways of  the  couutr}'  have  been  built  along  river  valleys,  so 
that  these  are  practicall}^  "  lines  of  least  resistance  "  to  the 
activities  of  a  people. 

QUESTIONS  AND  EXERCISES.— Under  what  conditions  and  at 
what  times  is  the  stream  with  which  you  are  best  acquainted  muddy  ? 

Note  and  describe  any  place  at  which  the  stream  is  cutting  away  its 
banks. 

Note  and  describe  some  place  where  sediment  is  being  deposited.  If 
possible,  account  for  the  action  in  each  case. 

An  embankment  of  freshly  turned  earth  receives  the  full  force  of  a 
rainfall ;  how  will  its  general  form  most  likely  be  affected  ? 

What  effect  has  sod,  shrubbery,  and  forestry  on  a  surface  that  is  ex- 
posed to  rain  ? 

Name  some  results  that  might  occur  if  the  channel  of  a  stream  were 
blocked  ? 

How  would  the  Mississippi  be  affected  if  the  Ozark  highlands  were 
elevated  considerably  higher  ?  (See  any  good  topographic  model  or  relief 
map.) 

What  effect  will  the  approaching  old  age  of  the  Mississippi  have  on 
the  size  of  the  Gulf  of  Mexico  ? 

On  p.  1 13  is  a  map  of  Chesapeake  Bay  ;  make  a  sketch-map  and  restore 
the  river  channels  on  the  supposition  that  the  surface  were  uplifted 
until  about  the  lowest  point  is  higher  than  sea  level. 


THE   WASTING    OF   THE   LAXD  :   RIVERS      127 

Does  the  appearance  of  the  Canon  of  the  Colorado  River  suggest  an 
abundant  or  a  scanty  rainfall?  How  would  a  great  increase  in  the 
rainfall  affect  the  scenery  so  far  as  the  topography  of  the  valley  is  con- 
cerned ? 

What  does  the  absence  of  tributaries  indicate  concerning  the  rainfall 
of  the  lower  Nile  ? 

From  the  cyclopaedia,  or  any  convenient  reference-book  obtain  a  de- 
scription of  the  Volga  and  its  delta. 

Make  a  list  of  ten  or  more  important  cities  situated  on  estuary 
mouths  ; — two  on  or  near  delta  mouths. 

COLLATERAL   READING. 

Shaler. — Aspects  of  the  Earth,  pp.  143-190. 

Mill.— Realm  of  Nature,  pp.  241-251. 

Davis. — Rivers  of  New  Jer.sey.  National  Geographical  Maga- 
zine. 

Redway. — Physioji:raphic  Geography  of  the  Mississippi  River. 
Proceedings  Engineers^  Club,  Philadelphia. 

Mississippi  River  Commission. — Map  of  the  Alluvial  Valley 
of  the  Mississippi  River. 

Powell.— Physiography  of  the  United  States,  Monograph  IL 

Russell. — Rivers  of  North  America. 


NOTES. 

^  On  an  average,  about  three  feet  of  water  fall  each  year  on  the 
land.  The  rate  is  not  uniform,  however,  l)ut  varies  from  a  frac- 
tion of  an  incli  to  about  fifty  feet.  Directly  and  indirectly  all 
the  water  of  tlic  laml  coiiics  from  the  sea  and,  sooner  or  later,  re- 
turns thereto. 

^The  t^rm  "  w;iter-shed  "  is  often  used  as  a  synonym  of  "di- 
vide."    Properly  used,  however,  it  is  not  a  divide  but  a  basin. 

^  There  are  a  few  instances  in  which  the  divide  is  so  ill-defined 
tliat  the  same  pool,  pond,  swamp,  or  stream  may  discharge  its 
waters  into  streiims  whose  mouths  are  at  a  great  distance  one 
from  the  other.  Tiius,  Two-ocean  Pond,  in  Vellowst(jne  National 
Park,  in  liigh-water  season,  has  two  <mtlets — one  through  tlie 
Yellowstone  to  the  Mississippi,  the  other  throiigii  the  Columbia. 


l;>8  PHYSICAL  GEOGRAPHY 

In  other  words  one  has  Athvntic,  the  other  Pacific  drainage.  The 
Cassiquiare  River  bifurcates,  discharging  simultaneously  into 
the  Orinoco  and  the  Rio  JVegro,  a  tributary  of  the  Amazon.  Be- 
tween the  headwaters  of  the  Parana,  and  those  of  the  southern 
tributaries  of  the  Amazon,  the  land  is  so  flat  that,  in  places,  the 
drainage  is  undecided. 

■*  The  cutting  and  the  carrying  power  of  water  depends  on  the 
speed  of  the  current.  A  slight  difference  in  the  velocity  makes  a 
very  great  difference  in  its  carrying  power.  Water  flowing  at  the 
rate  of  four  miles  an  hour  will  carry  sixty-four  times  as  mu.ch 
material  as  water  flowing  at  half  that  rate  of  speed  ;  that  is,  the 
carrying  power  varies  inversely  as  the  sixth  power  of  the  velocity. 

^  Silt  is  the  name  commonly  given  to  matter  held  in  suspension 
in  water ;  sediment  to  material  that  has  been  dropped.  The 
two  words  are  often  interchangeably  used. 

•^  Whichever  process  goes  on  at  any  particular  locality  depends 
on  the  velocity  of  the  current.  In  seasons  of  high  water  the  cur- 
rent may  remove  material,  while  at  low-water  stage  it  may  form 
a  bar.  That  is,  the  middle  course  of  a  stream  extends  much  fur- 
ther down  stream  in  high  than  in  low  water  periods.  In  short 
streams  that  flow  in  channels  of  considerable  slope  tliere  is  prac- 
tically but  one  course.  In  rivers  whose  waters  are  habitually 
clear  the  "  courses  "  are  rarely  ever  well  defined. 

^  Davis  cut-off  at  Palmyra  bend,  near  Vicksburg,  Mississippi,  is 
an  example.  The  distance  around  the  loop  was  twenty-two 
miles  ;  across  the  neck,  it  was  scarcely  half  a  mile.  An  obstruc- 
tion anchoring  in  mid-channel  forced  the  current  against  the 
narrow  neck,  and  the  latter,  little  l)y  little,  was  cut  away  by  the 
stream.  Finally  the  isthmus  was  sev^ered  and  the  whole  fiood  of 
the  river  very  quickly  poured  through  the  cut.  Around  the  loop 
the  fall  of  the  river  was  about  four  inches  per  mile  ;  through  the 
cut,  over  five  feet.  The  river  scoured  its  channel  about  one  hun- 
dred feet  in  depth,  and  so  swift  was  the  current  that  more  than 
a  week  elapsed  before  steamboats  could  ascend  it.  The  effect  of 
the  cut-off  was  far-i-eaching,  and  extended  both  above  and  below 
Palmyra  Bend  a  distance  of  over  one  hundred  miles. 

^  Such  a  stream  is  sometimes  called  a  consequent  river  because  its 
formation  is  consequent  upon  the  elevation  of  the  plain.  A  river 
is  an  antecedent  stream  when  its  existence  dates  before  that  of 
some  other  feature.     Thus  trreen  River  existed  before  the  forma- 


THE   WASTING   OF   THE   LAND  :    KIVERS      129 

tion  of  Uinta  Mountains,  and  with  respect  to  them  is  an  ante- 
cedent river. 

^  At  the  present  time  tlie  real  moutli  of  the  Hudson  is  near 
Troy.  Below  this  point  the  river  is  an  arm  of  the  sea,  swept  by 
tides  throughout  the  whole  distance.  This  singular  condition  is 
due  to  the  fact  that  the  lower  part  of  the  river  has  been  sub- 
merged, since  Glacial  times.  The  explorations  of  the  U.  S.  Coast 
Survey  have  disclosed  the  old  channel  of  Hudson  River  from 
lower  2y"ew  York  Bay  a  distance  of  nearly  eighty  miles  to  the 
southeast.  Were  this  part  of  Atlantic  coast  again  to  be  raised, 
it  is  not  unlikely  that  the  river  would  recover  its  long-buried 
channel. 

'"  At  the  point  where  the  angle  in  the  ledge  is  formed,  the  reces- 
sion since  1875  has  been  more  than  two  hundred  feet ;  at  the 
American  Fall,  since  1843,  it  has  been  very  slight.  It  is  a  ques- 
tion of  time  only  until  the  Canadian  Fall  shall  have  receded  to 
a  line  between  Duflferin  and  Sister  Islands.  When  this  has  taken 
place  the  American  Fall  will  have  nearly  or  quite  disappeared. 
Had  the  conditions  of  a  hard  stratum  at  the  top  and  a  softer  one 
at  the  bottom  been  reversed,  there  would  now  be  no  cataract, 
even  had  there  been  one  at  the  beginning  of  tlie  present  epoch. 
The  softer  rock  would  have  been  worn  away  until  the  perpen- 
dicular front  had  become  an  incline  extending  to  a  point  below 
Whirlpool  Rapids  ;  and  instead  of  the  sublime  cataract,  there 
would  now  be  a  succession  of  rapids  like  those  which  mark  the 
passage  of  St.  Lawrence  River. 

"  In  several  other  localities  the  Columbia  has  cut  its  channel 
through  similar  obstructions.  In  at  least  one  case  the  river  re- 
claimed its  former  channel  by  cutting  through  the  entire  thick- 
ness of  lava,  to  a  depth  of  about  2,500  feet ;  at  the  two  "cascades  " 
the  river  is  attempting  to  cut  its  channel  through  coulees  of  lava 
that  flowed  across  its  channel.  Deschutes  River,  a  tributary  of 
the  C(jlumbia,  is  readjusting  itself  by  cutting  a  new  channel  into 
the  same  sheet  of  lava. 


I''    Greenwich      60^ 

"X.^  Lincoln  Sea    c^ 


,*  GREi 

h     SI 


((FALKLAND  IS. 


A  ^'^  T  A 


R  C  T  I  C 


O  CEA 


.V 


r 


RIVER 

AND  Dl 


150^     Longitude     120'  West       fiom  90'     Greenwich      60^ 


CHAPTER  YIII 

THE  WASTING  OF  THE  LAND  :    THE  WORK  OF  UNDER- 
GROUND WATERS 

Probably  almost  as  much  water  sinks  into  the  porous 
rock  and  the  innumerable  crevices  of  the  rock-envelope  as 
gathers  in  the  various  external  channels.  The  work  of 
telluric,  or  underground  waters  may  not  be  quite  so  active 
in  degrading  the  rock  envelope  as  are  the  surface  streams, 
but  they  are  nevertheless  important  factors  in  the  physio- 
graphic processes  that  shape  the  earth's  topography. 
Surface  streams  flow  quickly  away  in  their  channels,  but 
the  underground  waters  must  trickle  slowly  through  chan- 
nels that  are  ill-adapted,  spending  their  energy  not  only 
in  forcing  their  way  through  passages  that  perhaps  are 
self-made,  but  also  in  keeping  the  passages  clear  of  ob- 
structions. The  work  of  surface  waters,  therefore,  is  com- 
paratively easy  and  simple  ;  that  of  undergroimd  drainage 
is  vastly  more  difficult. 

If  the  prevailing  rock  of  a  region  be  mainly  of  cla}',  or 
slate,  or  other  impervious  rock,  the  undergi'ound  di'ainage 
will  be  close  to  the  surface,^  for  such  rocks  not  only  pre- 
vent the  passage  of  water,  but  they  are  also  insoluble.  In 
such  cases  the  water  must  trickle  through  the  top  soil  much 
in  the  same  way  that  water  passes  through  a  filter  made  of 
sand  and  gravel — that  is,  it  must  flow  in  the  spaces  be- 
tween the  particles  of  rock  waste. 

On  the  other  hand,  if  the  rock  of  a  region  is  mainly  of 
limestone,  and  more  especially  if  the  strata  be  broken  and 

132 


UNDERGROUND   WATERS  133 

faulted,^  undergroimd  drainage  is  apt  to  be  verj  extensive. 
Not  only  does  the  water  clear  a  passage  for  itself  along  the 
lines  where  the  rock  is  broken,  but  it  also  dissolves  enough 
of  the  limestone  to  make  caverns  of  vast  extent. 

It  must  not  be  assumed,  liowever,  that  these  waters  al- 
ways remain  underground.  On  the  contrary,  the}'  are  con- 
stantly in  motion,  and  they  fiually  emerge  from  their  chan- 
nels to  reach  the  surface.  In  the  study  of  underground 
waters  they  may  be  considered  of  three  kinds,  namely — 
percolating  waters,  sj)rin(js  and  artesian  ivells,  and  under- 
ground streams. 

Percolating  Waters. — When  water  sinks  into  porous 
ground  it  tills  the  spaces  between  the  grains  of  sand,  gravel, 


Walcr  Level 
Spriiiffs 


DIAGRAM   SHOWING   THb    FLOW   OF   l^HRCOLATING   WATERS 

or  other  soil.  Some  soils  are  so  porous  that  a  cubic  foot 
will  contain  more  than  one-quarter  of  its  bulk  of  water. 
The  latter  sinks  through  the  ground  until  it  meets  a  layer 
of  rock  or  clay  through  wdiich  it  cannot  pass.  It  therefore 
accumulates  until  its  level  is  as  high  as  the  rim  of  the  im- 
pervious stratum. 

Flowing  over  the  lowest  part  of  this  rim,  it  goes  on,  per- 
haps to  fill  a  similar  basin  lower  down  the  slope,  or  possi- 
bly it  comes  to  the  surface  in  the  form  of  a  swamp,  a  pond, 
or  a  lake.  If  the  ])lain  or  slope  is  traversed  by  a  river  val- 
ley a  great  deal  of  the  water  oozes  through  the  soil  into  the 
stream.  In  many  instances  waters  of  percolation  are  the 
chief  supplies  of  streams.' 


134  PHYSICAL   GEOGEAPHY 

Wells  are  always  filled  by  percolatiug  waters,  and  to  ob- 
tain an  abundant  supply  it  is  necessary  only  to  sink  a  shaft 
to  some  point  l)elow  the  level  of  the  water.  Unless  the 
well  is  so  shallow  as  to  catch  the  surface  drainage,  the  water 
is  usually  cold  and  wholesome.  The  water  of  shallow  wells 
is  apt  to  be  impure. 

If  the  area  of  porous  soil  is  large  and  has  a  considerable 
depth,  an  enormous  quantity  of  water  may  be  held.  The 
City  of  London,  with  its  six  millions  of  people,  is  supplied 
with  water  that  percolates  through  the  adjacent  chalk-beds, 
and  the  water  supplies  of  many  of  the  towns  and  villages 
of  the  high  plains  east  of  the  Ilocky  Mountains  are  de- 
rived in  a  similar  manner. 


THK   WATER   SUPPLY   OF   LOW   SANDY    ISLANDS 
The  lighter  freih  water  rests  on  the  sea  water. 

The  "  sand  valleys  "  of  Western  Kansas,  Nebraska,  and 
Dakota  furnish  an  excellent  example  of  percolating  waters."* 
The  storm  waters  falling  in  these  valleys  are  almost  all  ab- 
sorbed and  held  in  suspension  by  the  deep  deposits  of  light, 
pulverulent  rock  waste.  During  dry  seasons  the  waters  of 
these  reservoirs  are  about  the  only  supply  to  the  people 
living  in  that  region.  The  amount  thus  held  in  the  porous 
rock  waste  is  generally  sufficient  to  irrigate  the  crops  that 
otherwise  would  perish  from  drought. 

The  water  supply  of  small  and  low  islands  is  obtained  in 
a  similar  manner.  The  storm  waters  fall  on  the  island 
and  immediately  sink  into  the  sand  until  they  reach  salt 
water.  But  inasmuch  as  the  fresh  water  is  the  lighter  of 
the  two,  it  rests  upon  the  surface  of  the  salt  water  without 
mixing  with  the  latter. 


UNDERGROUND    WATERS 


135 


In  many  instances  the  underground  waters  are  confined 
between  inclined  strata  of  impervious  rock.  In  such  a 
case,  if  the  porous  hiyer  be  tapped  by  a  boring,  the  water 
is  forced  up  througli  the  shaft  to  its  normal  level.  Arti- 
ficial spriugs  of  this  character  are  called  artesian  ruells. 
The  "  driven  "  or  "  piped  "  wells  so  common  throughout 
the  Mississippi  Valley  and  the  prairie  region  are  examples 
of  such  wells.  They  are  shallow,  however,  and  tap  only 
the  superficial  percolating  waters.  The  water,  moreover, 
is  usually  brought  to  the  surface  by  ordinary  lifting  pumps ; 
it  is  very  rare  that  such  wells  are  "  spouters." 

In  the  case  of  wells  sunk  to  a  depth  of  two  thousand 
feet  or  more,  the  water  in  many  instances  is  thought  to 


THE   WATER   SUPPLY   OF   ARTESIAN   WELLS 
The  porous  stratiiiu  is  both  covered  and  underlaid  with  impervious  rock. 


be  forced  above  the  surface — not  by  gravit}^,  as  is  com- 
monly supposed,  but  by  the  pressure  of  the  air  or  other 
gases  within  the  reservoirs. 

Along  the  low  coast  plain  of  Southern  California  several 
hundred  shallow  artesian  wells  have  been  driven,  and  many 
acres  have  been  made  productive.  The  first  wells  were 
spouters,  but  at  present,  in  nearly  every  instance  the 
water  must  be  pumped  to  the  surface.  Many  such  wells 
have  been  bored  in  the  Sahara.^ 

Springs. — A  small  stream  of  water  issuing  from  the 
ground  is  called  a  spriiuj.  In  some  cases  the  wattn-  spurts 
from  a  sloping  wall,  such  as  the  face  of  a  cliff,  but  in  gen- 
eral, it  gushes  out  of  comparatively  level  ground  near  the 


136  PHYSICAL   GEOGRAPHY 

foot  of  a  slope.  Usually  the  discharge  does  not  amount  to 
more  than  a  few  gallons  per  minute,  but  in  a  few  instances 
it  is  sufficient  to  fill  the  channel  of  a  good-sized  stream.*^ 

The  storm  waters  that  fall  on  porous  soil  sink  until  they 
come  to  rock  through  Avhich  they  cannot  pass,  and,  flowing 
along  the  surface  of  this  impervious  layer,  finally  emerge 
to  the  surface  at  some  distance  lower  down.  In  the  mean- 
time, if  the  water  has  been  able  to  make  a  free  channel 
instead  of  slowly  percolating  through  the  ground,  it  be- 
comes a  spring. 

As  a  rule  every  spring  makes  its  own  channel.  Usually 
the  force  of  the  flowing  water  is  sufficient  to  carry  away 
the  lighter  and  finer  material,  thereby  not  only  forcing  a 
passage,  but  keeping  it  clear  afterward ;  but  in  many  cases 
the  water  makes  a  channel  by  dissolving  a  part  of  the  rock 
through  which  it  flows.  If  the  quantity  of  material  dis- 
solved be  considerable,  mineixil  springs  result.  Such 
springs  are  very  common.  Those  at  Saratoga,  Vichy,  and 
Carlsbad,  are  known  all  over  the  civilized  world. 

In  volcanic  regions,  where  the  rocks  are  apt  to  be  seamed 
Avith  fissures,  the  water  trickles  downward  until  it  comes 
in  contact  with  heated  rocks,  and  when  it  again  emerges 
to  the  surface  the  water  may  be  at  a  boiling  temperature. 

So  long  as  the  mouth  of  a  spring  is  lower  than  the  sur- 
face of  the  waters  from  which  it  is  derived,  the  spring  will 
continue  to  flow,  and  will  be  a  constant  spring.  If  it  be 
situated  in  a  region  of  periodical  rains  it  is  apt  to  be  a 
periodical  sprmj/— flowing  during  the  rainy  season  only. 
If  the  flow  depends  partly  on  the  pressure  of  air  or  other 
gases,  an  intermittent  spring  may  be  formed.' 

Geysers. — In  several  volcanic  regions  there  are  hot 
springs,  which  at  intervals  eject  copious  quantities  of  hot 
water  and  steam.  The  eruptions,  unlike  volcanic  out- 
bursts, occur  with  almost  clock-like  regularity. 


UNDERGROUND   WATERS 


137 


The  geyser  differs  from  other  hot  springs  in  having  a 
long,   irregular  tube  that  extends  deep  into  hot  volcanic 
rocks.    The  tube  is  formed 
probably    by     the    spring 
water  itself,    which,  when 
very  hot,  dissolves  a  con- 
siderable   amount    of    the 
mineral  silica  but  deposits  ^, 
it  on  cooling. 

The  water  that  gradually 
collects  in  the  lower  part 
of  the  tube  in  time  is  heated 
far  beyond  the  temperature 
at  which  water  ordinarily  t 
boils.  For  a  considerable 
time,  the  weight  of  the  water 
in  the  upper  part  of  tlie 
tube  prevents  boiling  in 
the  lower  part.  Finally  a 
small  amount  of  steam  is 
formed,  and  some  of  the 
water  is  forced  out  at  the 
top  of  the  spring.  As  soon 
as  this  occurs,  the  pressTire 
at  the  lower  part  being  re- 
lieved, the  water  below, 
that  has  been  heated  far 
above  the  boiling  point, 
flashes  into  steam  —  not 
gradually  but  instantly. 

Erujotive  springs  of  this  character  are  not  common,  and 
there  are  but  three  regions  known  in  Avhich  they  have  been 
found — Iceland,  Yellowstone  National  Park,  and  Nortliern 
New  Zealand.     Hot  mineral  s[)rings  occur  in  many  other 


A    GEYSER,    YELLOWSTONE  NATIONAL 
PARK 


138  PHYSICAL   GEOGRAPHY 

localities,  but  they  are  not  eruptive.  The  geyser  region  of 
Iceland  has  been  known  for  more  than  a  centui-y.  It  is 
situated  near  the  group  of  active  volcanoes  and  covers  an 
area  of  two  or  three  square  miles.  There  are  about  one  hun- 
dred eruptive  springs,  one  of  which,  Grand  Geyser,  spouts 
a  column  of  water  and  steam  to  a  height  of  one  hundred 
and  forty  feet.  The  New  Zealand  group  is  situated  near 
the  volcano  Tarawera.  It  is  small  in  area,  and  contains 
but  few  spouting  springs. 

The  geyser  region  of  the  Yellowstone  National  Park, 
Wyoming,  contains  several  groups,  mainly  in  the  basin  of 
Firehole  Eiver.  It  comprises  more  than  ten  thousand 
geysers  and  hot  springs.  Of  this  number  about  two  score 
discharge  water  to  a  height  of  one  hundred  feet  or  more  ; 
one,  the  Giantess,  spouts  a  column  of  water  two  hundred 
and  fifty  feet  high,  while  the  steam  is  forced  nearly  a  thou- 
sand feet  higher.  The  eruptions  occur  at  periods  varying 
from  thirty  minutes  to  about  as  many  hours.  Each  is  pre- 
ceded b}^  a  gentle  ovei-flow  of  water,  and  commonly  lasts 
from  a  few  seconds  to  fifteen  minutes,  but  in  a  few  instances 
continues  for  more  than  two  hours.  The  intervals  between 
eruptions  rarel}^  vary  more  than  a  few  minutes,  but  care- 
ful observations  show  that  their  length  is  increasing,  and 
the  energy  of  eruption  is  diminishing. 

The  deposition  of  silica  from  the  cooling  waters  takes 
fantastic  forms.  In  many  instances  the  rock  thus  produced 
is  richly  colored  with  variegated  bands.  The  "  Pink-and- 
White  Terraces  "  of  New  Zealand  derive  their  name  from 
this  fact. 

Mud  Volcanoes.— Mud  "Volcanoes"  are  hot  springs 
that  have  piled  cone-shaped  mounds  of  mud  about  their 
vents.  The  mud  hardens  into  a  compact  mass.  Steam 
and  sulphurous  gases  are  commonly  the  products  of  these 
alleged  volcanoes.     The  energy  displayed  is  feeble,  and 


UNDERGEOUXD    WATERS  139 

the  mud  cones  are  seldom  more  tliau  twenty  or  thirty  feet 
high.  The  mud  consists  of  fine  clay  formed  from  the  min- 
eral matter  of  the  spring.  Mud  volcanoes  are  common  in 
all  volcanic  regions. 

Underground  Streams. — In  addition  to  the  multitude 
of  surface  streams,  a  large  part  of  the  water  finds  its  way  to 
the  sea — not  simply  by  percolation  but  in  underground 
streams.  Undoubtedly  the  run-off  of  most  streams  is 
mainly  above  ground,  but  at  the  same  time,  a  considerable 
part  of  their  waters  flows  below  the  surface. 

There  are  several  reasons  for  this.  In  the  first  place, 
whenever  a  stream  flows  in  a  gravelly  channel,  a  great  deal 
of  the  water  must  necessarily  sink  into  the  gravel  and  flow 
along  the  old  bed-rock  bottom.  The  same  is  equally  true 
in  the  case  of  rivers  that  flow  through  light,  sandy  rock 
waste,  such,  for  instance,  as  those  of  the  Basin  Region, 
west  of  the  Eocky  Mountains.  The  underground  flow  of 
such  rivers  is  strong  even  when  fierce  summer  heat  has 
evaporated  their  surface  waters.^ 

In  many  cases,  too,  small  river  channels  have  been  ob- 
literated for  one  purpose  or  another.  Noav,  although  the 
surface  flow  may  be  destroyed  the  underground  current  is 
not ;  on  the  contrary,  it  is  apt  to  be  strengthened.  Thus, 
in  some  of  the  larger  cities  many  small  drainage  courses 
have  been  covered  up  in  grading  the  streets,  and  in  several 
instances  it  has  been  found  necessary  to  excavate  these  old 
water-courses  and  sewer  them. 

In  New  York  and  London  the  channels  of  many  such 
streams  have  been  plotted,  and  drainage  maps  showing  their 
former  courses  are  used  by  the  Boards  of  Health  in  sanitary 
investigation.  In  several  instances  these  streams,  becom- 
ing obstructed,  have  forced  their  way  to  the  surface  and 
flooded  the  streets  with  a  deluge  of  water.  Such  experiences 
are  not  uncomiiiou  ;  they  occur  in  almost  every  large  city.' 


uo 


IMIYSKIAL   (lEOGRAPHY 


Of  still  greater  interest,  though  not  more  important,  are 
the  various  "  Lost  "  rivers.  These  streams  receive  their 
name  from  the  fact  that  for  part  of  their  courses  they  are 
ordinary  surface  streams  ;  for  the  rest,  they  How  through 
subterranean   channels.     In  some  instances   the  water  of 


A  SINKHOLE,   EDMUNSON   COUNTY,    KENTUCKY 
The  Ihroat  leading  to  the  cavern  below  has  been  artificially  closed. 


the  river  disappears  by  percolation  ;  in  most  instances  the 
stream  pitches  headlong  into  a  "  sinkhole." 

In  the  limestone  area  of  southern  Indiana,  Kentucky, 
and  Tennessee,  underground  rivers  are  very  common.io 
One  of  these  rivers  Avinds  its  Avay  beneath  the  floor  of 
Mammoth  Cave.  Its  waters  contain  a  species  of  fish  and 
two  or  three  of  insect  life   that   have   rudimentary   eyes 


UNDERGROUND   WATERS  141 

only — and  indeed  they  have  no  use  for  perfect  organs,  for 
never  a  ray  of  light  penetrates  to  their  abode. 

Similar  streams  are  found  in  Weir's  Cave,  in  Luray  Care, 
and,  in  fact,  in  almost  every  limestone  cavern.  In  Derby- 
shire, England,  the  Hampo  and  the  Manifold  flow  manj- 
miles  each  through  an  underground  passage.  In  both  in- 
stances the  identity  of  the  stream  is  proved  by  throwing  a 
floating  body  into  the  water  above  the  beginning  of  its 
underground  course  and  capturing  it  when  it  reap^jears. 

In  Southern  California,  where  water  is  required  for  ir- 
rigation, underground  streams  have  been  captured  and 
forced  to  the  surface.  This  is  accomplished  by  building  a 
dam  across  the  stream  at  a  point  Avhere  it  emerges  from 
the  canon  to  the  open  plain.  The  dam  extends  from  the 
surface  of  the  ground  down  to  bed-rock.  The  water  is 
thereby  forced  to  the  surface. 

It  is  noticeable  that  where  such  submerged  dams  are 
constructed,  the  artesian  wells  in  the  plain  below  are  seri- 
ously impaired — the  flow  of  water  being  greatly  reduced — 
all  of  which  seems  to  show  that  underground  waters  have 
a  much  greater  circulation  than  is  generally  imagined. 

Physiography  of  Underground  Waters.  —  Although 
the  work  of  underground  waters  is  by  no  means  so  extensive 
as  those  flowing  above  the  surface,  they  are  nevertheless  of 
great  importance  especially  from  an  economic  point  of  view. 
Under  almost  any  conditions  water  has  a  considerable  sol- 
vent power,  and  hot  w^ater,  especially  if  under  pressiu'e,  will 
dissolve  many  kinds  of  rock  that  are  not  affected  by  cold 
water;  when  the  solution  cools,  however,  much  of  this 
matter  is  again  freed  from  solution.  In  the  meantime,  if 
the  water  has  been  forced  to  the  surface,  the  substances 
dissolved  Avill  be  carried  along  and  there  deposited. 

Sometimes  the  deposits  are  spread  liap-hazard  over  the 
surface  of  the  gi-ound,  forming  sinter  or  tufa.     If  the  latter 


142  PHYSICAL   GEOGRAPHY 

happens  to  cover  loose  rock  waste  or  soil,  a  cavern  or  cave 
will  result  if  the  material  under  it  be  removed. 

In  other  instances  the  hot  waters,  charged  with  mineral 
or  metahic  salts.  How  into  deep  fissures  in  the  rocks.  As 
the  water  cools  the  soluble  matter  is  deposited  on  the  walls 
of  the  fissure  until,  finally,  the  latter  is  filled,  thereby 
forming  a  mineral  vein  or  lode.     All  through  the  various 


BLUE  GROTTO,    ISLAND   OF   CAPRL    ITALY 

mountain  regions  of  the  earth,  gold,  silver,  copper,  lead, 
and  other  valuable  metals  have  been  deposited  in  such 
fissures  and  veins."  Thus  underground  waters  are  a 
vehicle  by  which  many  useful  metals  are  carried  from  the 
interior  to  the  surface  of  the  earth. 

Caverns. — Caverns  and  caves,  although  sometimes 
formed  at  the  surface  in  the  manner  already  noted,  for  the 
greater  part  are  formed  underground  by  the  action  of 
■water.''     The  water  merely  dissolves  the  rock  and  carries 


UNDERGROUND   WATERS 


1^3 


it  off,  leaving  a  cavern.  Clay, 
slate,  granite,  and  sandstones  are 
not  readily  dissolved ;  and  in  re- 
gions underlaid  by  such  rocks, 
caverns  are  rare.  Limestones,  on 
the  contrary,  are  quite  soluble, 
and  in  localities  where  they  are 
the  prevailing  rock,  caves  and 
caverns  are  common.  In  the  cav- 
ern district  of  Kentucky,  Tennes- 
see, and  Virginia'^  small  pieces 
of  sharp  flint  are  plentifully  dis- 
tributed throughout  the  lime- 
stone. These  are  tossed  about 
and  carried  along  with  the  water 
and  thus  become  powerful  cutting 
tools. 

Between  the  solvent  power  of 
the  water  and  the  incessant  cut- 
ting done  by  the  flint  particles, 
the  underground  channel  is  worn 
deeper  and  wider  till  a  cavern, 
perhaps  a  score  of  miles  long  and 
many  feet  deep,  is  formed.  Very 
likely  it  has  hundreds  of  galleries 
and  branches  ;  time  alone  is  nec- 
essary to  give  it  vast  dimensions. 

But  time  alone  will  see  the  fac- 
tors that  made  the  cavern  destroy 
it.  In  the  first  jjlace  the  surface 
waters  are  constantly  at  Avork 
wearing  away  the  rock  that  forms 
the  roof  or  dome  of  the  cavern. 
By    and    by    breaks     arc    made 


L 


144 


PHYSICAL   GEOGRAPHY 


tlirougli  tliG  roof  aud  siukboles  are  thus  formed.  These 
increase  in  size  and  in  number  until  the  dome  is  destroyed. 
The  river  is  then  no  k)nger  an  underground  stream ;  it  is  a 
surface  river  flowing  in  a  limestone  canon.  Natural  Bridge, 
in  Virginia,  is  a  remnant  of  one  of  these  domes  ;  the  rest  of 
the  roof  has  been  carried  away." 

In  the  second  place,  parts  of  these  caverns  are  filled  up  by 


A   PASSAGE   IN    LURAY   CAVERN-STALACTITES   AND  STALAGMITES 

the  limestone  itself.  In  places  the  water  charged  with  lime- 
stone leaks  or  filters  through  at  the  top  of  the  dome,  fall- 
ing drop  by  drop.  A  part  of  the  water  leaves  a  minute 
portion  of  limestone  at  the  roof ;  the  rest  falls  to  the  floor 
of  the  cavern,  where  a  little  more  of  the  water  evaporates. 
So,  little  by  little,  the  deposited  limestone  gathers  into 
icicle-shaped  columns,  both  at  the  roof  and  the  floor  of  the 


UNDERGROUND   WATERS  U5 

caveru.  The  former  are  called  stalactites,  the  latter  stalag. 
mites.  In  time  the  two  join,  forming  a  single  column,  and 
as  the  water  trickles  down  their  sides  they  increase  in  size, 
and  thus  the  cavern  is  filled. 

Perhaps,  in  the  course  of  time,  this  same  mass  of  lime- 
stone may  be  dissolved  away  and  redeposited  elsewhere. 
At  all  events,  the  process  illustrates  the  general  law  that 
governs  cavern-formation  in  these  regions.  Water  in  mo- 
tion dissolves  limestone  and  makes  caverns ;  still  water  de- 
posits limestone  and  fills  them  7ip^^ 

QUESTIONS  AND  EXERCISES.— If  possible  find  the  depth  of  each 
of  half  a  dozen  or  more  wells  in  the  neighborhood  in  which  you  live : 
compare  the  distance  of  the  surface  of  the  ground  to  the  surface  of  the 
water  in  the  wells. 

To  what  depth  must  a  well  be  sunk  before  it  will  fill  with  water  ? 

Will  one  be  apt  to  find  percolating  waters  in  regions  having  but  a 
very  little  rain  ? 

Explain  why  water  in  very  shallow  wells  is  apt  to  be  impure 

How  do  springs  become  "  mineral  "  in  character  ? 

Why  does  rain  water  contain  no  mineral  matter  in  solution  ? 

Why  are  geysers  and  hot  springs  confined  usually  to  volcanic  regions? 

Under  what  circumstances  or  conditions  can  water  be  heated  above 
the  ordinary  boiling  point  ?     (See  almost  any  text-book  in  physics.) 

From  the  diagram,  p.  129,  decide  the  conditions  which  will  cause 
underground  streams  or  percolating  waters  to  form  a  swamp. 

Describe  a  way  in  which  caverns  may  be  formed  at  the  foot  of  sea 
cliffs  that  face  heavy  waves. 

How  are  the  sinkholes  in  the  limestone  regions  formed  ? 

By  using  lime-water  such  as  is  obtainable  at  the  druggist's,  suggest 
a  way  in  which  stalactites  may  be  artificially  formed. 

COLLATERAL   READING. 
Shai.kr.— First  Book  in  Geology,  pp.  66-87. 
Shalkr. — Aspects  of  tlic  Eartli,  i)p.  !)<J-142. 
Powell.— Irrif^iition  und  Artesian  Wells,  pp.  203-290.      United 

States  Oeolor/ical  Snrfiey,  1 1th  Annital  Report,  Part  2. 
Lk  Coxte. — Elements  of  Geology,  pp.  10.3-1  IJJ. 
United  States  Geological  Survey.— Map  of  Yellowstone 
National  Park. 


UG  PHYSICAL   GEOGRAPHY 


NOTES 

^  If  the  rocks  are  near  the  surface  and  the  amount  of  water  is 
considerable,  swamps  may  result.  That  is,  swamps  may  be  an 
incident  of  imperfect  underground  drainage,  as  they  are  of  im- 
perfect surface  drainage. 

^  The  fissures  between  the  ends  of  faulted  strata  are  very  fre- 
quently the  channels  of  springs,  and  sooner  or  later  the  fissure  is 
likely  to  be  closed  up  by  deposits  from  the  spring  water. 

3  This  may  be  seen  in  the  cases  of  streauis  that  flow  through  a 
region  of  pervious  soil.  Such  streams  steadily  increase  in  volume, 
although  for  many  miles  they  receive  no  tributaries.  As  an  ex- 
ample, Spanish  Fork,  on  the  west  slope  of  the  Wasatch  Mountains, 
/  eceives  only  two  or  three  small  tributaries  from  the  summit  to 
the  base  of  the  mountains.  It  begins  as  a  rivulet,  scarcely  larger 
than  one's  arm  ;  it  reaches  the  base  of  the  range,  a  mountain  tor- 
rent twenty  feet  across.  Almost  the  whole  increment  is  due  to 
percolation. 

^  The  sand  valleys  are  apparently  Jiills,  but,  in  most  cases 
they  are  valleys  filled  with  rock  waste  carried  thither  by  winds. 
In  the  saturation  of  these  accumulations  of  rock  waste  capillary 
attraction  is  an  important  factor  ;  for  this  little-understood 
force  is  not  only  an  agent  of  accumulation,  but  one  of  reten- 
tion also. 

5  The  amount  of  desert  land  made  ijroductive  solely  by  artesian 
wells  has  been  greatly  exaggerated  by  senseless  guesses.  Such  es- 
timates commonly  make  the  aggregate  as  ' '  millions  of  square 
miles."  As  a  matter  of  fact  all  the  artesian  wells  in  the  world 
do  not  supply  an  area  equal  to  that  of  the  State  of  Delaware  with 
the  water  necessary  to  produce  the  whole  of  its  crops. 

^  The  difference  between  springs  and  percolating  waters  is 
mainly  one  of  degree  ;  issuing  from  a  channel  it  is  a  spring,  but 
if  the  water  merely  oozes  through  the  soil  it  is  considered  only 
as  an  example  of  percolation.  In  Florida  there  are  a  number  of 
springs,  so-called,  that  discharge  each  an  amount  of  water  suffi- 
cient to  fill  a  river  bed.  Orange  and  Silver  Springs  are  so  large 
that  small  river  craft  easily  enter  the  mouths.  These  springs,  as 
a  matter  of  fact,  are  the  exits  of  underground  rivers. 

^  From  time  immemorial  geographers  have  explained  the  peri- 


UNDERGROUND    WATERS  147 

odieal  spring  on  tlie  supposed  existence  of  a  siphon-shaped  chan- 
nel. Doubtless  such  channels  exist,  but  not  a  single  one  has  ever 
been  discovered.  In  a  tew  instances  the  pressure  ot  accumulating 
gases  is  known  to  be  a  cause  ot  uiteruiittent  How,  but  in  tlie  great 
majority  of  cases  the  cause  of  periodicity  is  unknown.  One  of  the 
most  remarkable  periodical  springs  occurs  in  Palestine  near  the  old 
convent  of  Mar  Jirius.  This  spring  is  quiescent  for  about  two  and 
a  half  days,  and  its  period  of  activity  lasts  for  several  hours.  It 
is  probable  that  the  stream  flowing  from  this  spring  is  the  Sab- 
batic River  described  by  Josephus,  which  rested  for  six  days  and 
flowed  on  the  seventh.  The  fact  that  such  springs  gradually  de- 
crease their  periods  ot  quiescence,  and  finally  become  regular, 
bears  out  this  supposition .  A  spring  near  Rogersville,  Tennessee, 
IS  celebrated  for  the  enormous  quantity  of  water  ejected.  Its 
period  of  flow  occurs  about  every  half  hour,  lasting  only  a  few 
minutes.  The  Bullerborn,  once  a  famous  intermittent  spring  of 
Westphalia,  has  now  a  constant  flow.  In  regions  of  very  high 
tides,  periodical  springs  are  sometimes  formed  by  tidal  action. 
The  fresh  water  is  pushed  back  by  the  tide,  until  it  emerges  to 
the  surface  through  self-made  channels. 

»  In  desert  regions,  where  the  heat  is  intense,  there  are  many 
instances  of  rivers  that  are  dry  "  washes"  in  the  daytime,  and 
fair-sized  streams  at  night.  Water  nearly  always  can  be  found 
at  a  slight  depth,  by  digging  for  it.  In  the  daytime,  the  enor- 
mous evaporation  causes  the  water  to  disappear.  In  the  night, 
or  during  cloudy  days,  the  evaporation  is  lessened  and  the  perco- 
lating waters  rise  to  the  surface.  This  phenomenon  is  occasion- 
ally noticed  in  the  lower  courses  of  Humboldt,  Carson,  and  Reese 
Rivers,  in  Nevada.  Tla;  underground  part  of  the  river  is  nearly 
always  to  be  found. 

'•'  Considerable  trouble  from  this  cause  occurred  near  the  junc- 
tion of  Oxford  Street  and  Edgeware  Road,  London,  and  the  rea- 
son was  the  fact  that  the  famous  Tyburn  flowed  in  this  locality, 
crossing  Oxford  Street  a  little  to  tlie  eastward  of  the  entrance 
to  Hyde  Park.  Aljout  four  liundred  square  feet  of  Broad- 
way, New  York,  recently  caved  in  from  a  similar  cause.  The 
foundations  of  a  costly  church  in  Philadelphia  sank  in  the 
(liiicksaiid  before  they  were  complete<l,  and  the  large  sewer  under 
one  of  tlie  [JiincipMl  streets  li;is  caved  in  several  times— all  be- 
cause they  were  nnilciinincd  li\'  Imried  streams. 


148  IMIVSIOAL   GEOGKAPHY 

"'At  Orangovillo,  Indiana.,  an  underground  stream  comes  to 
tlie  surface  and  Hows  with  sufficient  force  to  turn  a  mill-wheel. 
Only  a  few  miles  away,  Lost  River,  a  considerable  stream,  sinks 
out  of  sight.  San  Pedro  Springs,  near  San  Antonio,  Texas, 
is  the  outlet  of  an  underground  stream.  Giant  Spring,  near 
Great  Falls,  Montana,  is  the  outlet  of  Little  Belt  River,  which 
disap[)ears  and  flows  underground  for  thirty  miles  of  its  course. 
in  Alabama,  the  engineers  of  the  Anniston  and  Atlantic  Railway 
discovered  an  underground  stream  sixty  feet  below  the  bed  of 
Coosa  River.  According  to  Greek  legends,  the  Alpheus,  the  river 
ot  Peloponnesus,  which  Hercules  turned  through  the  Augean 
stables,  .sank  underground  and  emerged  to  the  surface  somewhere 
in  Sicily.  As  a  matter  of  tact  a  considerable  part  of  the  course 
of  the  Alpheus  is  underground,  and  there  is  a  spring  in  Sicily 
discharging  a  large  volume  of  water.  It  is  hardly  necessary  to 
add  that  the  two  have  no  connection. 

"  As  a  rule  such  veins  have  a  very  symmetrical  banded  appear- 
ance, the  stripes  on  the  right  hand  corresponding  with  those  on 
the  left.     In  California,  these  veins  are  called  "ribbon  "  rock. 

'2  There  a,re  several  instances  in  which  eaves  have  been  formed 
in  volcanic  rocks.  Fingal's  Cave,  on  the  Island  of  Statfa,  west 
ot  Scotland,  is' an  example.  It  is  more  than  two  hundred  feet  in 
length,  and  is  surmounted  by  a  dome  sixty  feet  high.  In  many 
instances  waves  have  hollowed  out  caverns  in  rock  cliff's. 

^^  Mammoth  Cave,  Kentucky,  is  a  labyrinth  of  passages  aggre- 
gating more  than  two  hundred  miles  ;  the  length  of  the  cave  on 
a  straight  line  is  about  ten  miles.  Some  of  the  vaults  and  domes 
are  two  hundred  and  fifty  feet  high.  There  are  several  other 
eaves  in  the  vicinity  nearly  if  not  quite  as  large.  Weir's  Cave 
and  Luray  Cavern,  both  in  Virginia,  are  smaller  than  Mammoth 
Cave.  Being  limestone  caverns  they  do  not  differ  from  the  latter. 
Howe's  Cave,  Schoharie  County,  New  York,  is  one  of  the  few 
large  caverns  of  interest  in  the  northern  Appalachian  region.  In 
the  grotto  of  Lueg,  Illyria,  there  are  three  galleries,  one  over 
another.  The  cavern  of  Adelsberg,  Austria,  is  the  abandoned 
channel  of  the  Poik.  Its  length  is  not  far  from  two  miles  ;  its 
labyrinthine  passages  aggregate  many  miles.  A  considerable 
part  of  the  course  of  the  Poik  is  underground.  Probably  the  un- 
derground passage  and  caverns  of  the  Timavo  have  been  more 
thoroughly  investigated  than   those  of  any  other  stream.     The 


UNDERGROUND   AVATERS  149 

river  flows  to  the  Adriatic,  a  few  miles  north  of  Trieste,  and  its 
cliaracter  has  been  Ivnown  for  more  than  two  thousand  years. 
Coneerning  it  Virgil  wrote  : 

ct  fontem  superare  Timavi 
undo  i)cr  ora  novL-ni  vasto  cum  luurimire  nioutis 
it  mare  proruptiun,  et  pchii^o  premit  arva  sonanti. 

—^■Eneul  I  ,  247. 

Virgil's  description  is  no  longer  true  of  the  delta,  for  the  nine 
mouths  have  become  only  three  in  number. 

'*  Many  similar  natural  bridges  are  known  to  exist  in  various 
parts  of  the  world.  Near  Bogota,  Colombia,  a  natural  arch  spans 
a  chasm  nearly  four  hundred  feet  deep.  The  arch  is  a  double 
one,  the  lower  one  being  composed  of  three  large  fragments  that, 
detached  from  the  upper  arch,  fell  in  such  a  manner  as  to  wedge 
themselves  between  the  perpendicular  walls.  In  one  of  the  deep 
canons  of  Arizona  a  huge  mass  of  rock  has  fallen  and  become 
wedged  between  the  walls  of  the  chasm,  thereby  forming  a  sort 
of  natural  bridge.  A  natural  bridge  spans  Pine  Creek,  in  Gila 
County,  Arizona.  Ijike  that  in  V^irginia,  it  is  the  fragment  of  the 
dome  of  a  stream  that  once  flowed  underground.  The  arch  is 
about  four  hundred  feet  wide  and  the  span  is  about  a  thousand 
feet  in  length.  The  underside  of  the  arch  is  water- worn,  but 
since  it  was  formed  the  creek  has  cut  its  channel  more  than  two 
hundred  feet  downward.  In  several  instances  the  arch  more 
properly  constitutes  a  tunnel.  One,  near  Clinch  River,  Virginia, 
is  more  than  halt  a  mile  long,  and  is  a  part  of  the  route  selected 
for  a  railway,  in  almost  every  in.stance  a  stream  of  water  flows 
under  the  arch,  and  its  current  carries  away  the  fragments  that 
fall  from  the  roof. 

'^  The  distribution  and  also  the  concentration  of  certain  eco- 
nomic minerals,  in  many  instances,  has  resulted  from  the  flow  of 
underground  waters.  Gold  has  been  dissolved  from  certain  rocks 
and  gradually  concentrated  in  %'eins  through  their  action.  Iron 
salts  have  been  leached  from  rocks  and  deposited  in  other  rocks 
by  the  same  agency.  Beds  of  sand  through  which  water  con- 
taining lime  percolates,  in  time,  become  sandstone,  the  grains  of 
sand  being  cemented  together  by  the  lime  carried  in  the  water. 


CHAPTER  IX 

THE   WASTING   OF   THE   LAND:   THE   WOKK   OP 
AVALANCHES   AND   GLACIERS 

A  GREAT  deal  of  the  moisture  mingled  with  the  air  falls 
upon  the  laud  in  the  form  of  snow.  Excepting  very  cold 
regions,  the  snow  that  falls  at  altitudes  below  three  or 
four  thousand  feet  melts  with  the  coming  of  spring  and 
flows  away  in  the  various  stream  channels.  In  high 
mountain  regions  more  or  less  snow  falls  at  altitudes  in 
which  the  temperature  is  rarely  higher  than  the  melting 
point  of  the  snow.  In  such  localities,  therefore,  but  little 
of  the  snow  can  melt  where  it  falls.' 

In  the  Alps  and  in  the  higher  ranges  of  the  western 
United  States,  the  heaviest  snows  fall  between  the  altitudes 
of  six  thousand  and  nine  thousand  feet.  Very  little  accu- 
mulates below  four  chousand  feet,  and  but  little  falls  above 
twelve  thousand  feet ;  in  fact  but  little  moisture  exists  at 
such  high  altitudes. 

At  high  elevations,  even  though  the  fall  might  be  slight, 
it  would  seem  as  though  the  accumulation  would  increase 
until  the  mass  of  snow  exceeded  that  of  the  mountains. 
In  certain  polar  lands  it  is  possible  that  tliis  may  be  oc- 
curring, but  in  high  mountain  regions  various  agencies 
operate  to  prevent  such  enormous  accumulation.  Among 
them  are  evaporation,  wind,  avalanches,  and  glaciers. 
They  not  only  remove  the  snow  and  ice,  but  they  are  also 
powerful  factors  in  wearing  away  the  land  and  in  trans- 
porting rock  waste. 

150 


WORK   OF   AVALANCHES   AND    GLACIERS     151 


Evaporation  is  a  veiy  active  agent  in  the  removal  of 
snow.  Ice  and  snow  evaporate  just  as  does  water ;  and 
at  great  heights,  where  the  air  does  not  press  so  heavil}^  as 
at  sea-level,  evaporation  is  very  rapid.  This  is  seen  when 
frozen  roads  become  dry  and  dnstj  witliout  thawing.^ 

Winds  are  also  a  very  potent  factor.  In  high  mountain 
regions  the  wind  has  a  force  that  is  almost  unknown  in 
lowlands,  and  the  gales  that  rage  among  snow-covered 
peaks  quickly  clear  the  dry  snow-dust  from  every  exposed 
surface  and  drift  it  into  ravines  and  canons.^ 

There  are  two  factors  at  work,  however,  that  are  inter- 
esting, not  only  because  they  remove  an  enormous  amount 
of  snow,  but  also  because  in  transporting  it  they  become 
physiographic  agents  of 
very  great  importance. 
These  are  avalanches 
and  glaciers. 

Avalanches.  — When 
a  great  body  of  snow, 
resting  on  a  steep  slope, 
suddenly  slips  and 
plunges  down  the  in- 
cline, the  moving  mass 
is  called  an  avalanche, 
or  challanche.  Excepting 
the  matter  of  the  mate- 
rial transported,  whicli 
is  mainly  snow,  the  ava- 
lanche does  not  differ 
materially  from  an  ordi- 
nary landslide.  But 
while  it  is  very  rare  that  a  second  landslide  takes  place 
in  the  same  track,  it  is  evident  that  an  avalanche  may 
occur  every  time  the  snow  falls  on  the  slope.     The  snow 


AVAlANi.llL    BASIN,    MUM  ANA 

Tlie  slopes  art-  too  steep  to  permit  the  accumulation 
of  siiozo.  and  the  latter,  gathering;  -u'ltliin  the 
basin,  has  formed  the  lake  at  the  bottom  of  the 
clijf. 


153  PHYSICAL   GEOGRAPHY 

accumulates  ou  the  steep  slope  until  its  great  weight 
causes  it  to  slip,  aud  the  great  mass  gathering  speed, 
moves  downward  with  a  terrific  roar. 

lu  the  Ali)s,  where  as  a  rule,  the  slopes  are  steep, ^  such 
downfalls  take  place  frequently  and  regularly.  In  many 
places  the  avalanche  tracks  are  as  definitely  marked  as  the 
river  channels.  Indeed,  one  may  consider  the  avalanche 
track  as  the  torrential  part  of  a  stream  whose  flow  is  occa- 
sional and  spasmodic.  Like  the  mountain  torrent,  too,  it 
carries  to  lower  levels  an  enormous  amount  of  rock  waste 
stripped  from  the  slopes.  Not  only  are  avalanche  courses 
distinctly  marked,  but  expert  mountaineers  who  have  ac- 
quired experience  in  discerning  weather  signs  are  able  to 
predict  the  occurrence  of  the  snowslide  with  great  cer- 
tainty. The  avalanche,  therefore,  is  a  feature  of  mountain 
economy  not  less  normal  than  the  mountain  torrent. 

The  most  destructive  avalanches  occur  in  the  first  hours 
of  sunshine,  just  after  a  snow-storm.^  The  flakes  are  then 
so  fine  and  smooth  that  they  have  but  little  coherence,  and 
almost  any  disturbance  may  start  them.  The  footstep  of 
the  chamois  or  a  gust  of  wind  imparts  motion  to  a  handful 
of  snow,  and  it  begins  its  descent.  Gathering  fresh  mate- 
rial as  it  advances,  and  increasing  in  velocity  every  moment, 
it  soon  becomes  a  force  that  sweeps  everything  before  it, 
carrying  havoc  and  destruction  perhaps  into  the  region 
of  cultivated  fields  and  human  habitations,  far  beyond  the 
foot  of  the  slope.  Rocks  crash  right  and  left  and  the  whirl 
of  the  wind  carries  eddies  of  snow  a  thousand  feet  or  more 
into  the  air. 

When  avalanches  follow  their  customary  tracks  they  are 
neither  especially  dangerous  nor  destructive,  unless  the 
snow  and  rock  waste  reach  beyond  their  ordinary  limits. 
But  in  many  instances  they  have  taken  place  in  localities 
previously  free  from  them,  and  these  are  the  cases  in  which 


WORK    OF   AVALANCHES   AND    GLACIERS     153 

the  destruction  is  greatest.  Not  ouly  is  everything  de- 
stroyed along  the  path  of  the  moving  snow,  but  the  effects 
are  even  more  apparent  along  the  edges ;  for  the  blasts  of 
wind  set  in  motion  by  the  swiftly  mo^'ing  snow,  fell  every 
vestige  of  timber  a  thousand  feet  or  more  on  both  sides. 
In  recent  years,  places  that  the  experienced  mountaineers 
have  discovered  to  be  possible  avalanche  tracks,  have  been 
artificially  guarded,  so  as  to  prevent  the  formation  of 
dangerous  snowslides. 

Another  form  of  avalanche  occurs  in  the  Alps  late  in 
the  season,  at  the  beginning  of  warm  weather.  Instead  of 
light,  powdery  snow,  its  volume  consists  of  ice  and  coarse 
snow  mixed  with  rock  waste.''  The  lower  part  of  the  snow 
and  ice  are  undermined  by  water  as  the  ground  on 
which  it  rests  thaws.  Finally  the  Avhole  mass  slides  down 
the  incline.  These  avalanches  do  not  differ  in  any  ma- 
terial respect  from  landslides. 

Glaciers. — A  great  part  of  the  snow  that  falls  on  high 
and  steep  slopes  is  either  blown  into  ravines  by  the  wind 
or  is  tumbled  into  them  by  avalanclies.  In  the  upper 
part  of  the  ravine  the  snow  is  light  and  flaky,  but  farther 
down  it  has  begun  to  melt,  and  instead  of  crystals  it  con- 
sists of  little  granules  of  ice,  called  neve.  Still  farther 
down  the  ravine,  the  neve  has  a  striped  or  banded  appear- 
ance.^ Then  the  surface  takes  the  form  of  irregular  Avave- 
shaped  ridges,  and  finally  the  surface  is  a  field  of  ridges 
and  hummocks,^  half-drowned  in  streams  of  muddy  water, 
and  ending  in  a  mountain  torrent. 

All  this  mass  of  ice  and  snow  constitutes  a  glacier.  It 
is  in  motion,  and  excepting  the  velocity,  which  is  so  slow 
as  to  be  almost  imperceptible,  its  movements  are  much 
like  those  of  a  stream  of  water.  The  flow  is  faster  at  the 
surface  than  at  the  bottom,  and  it  is  also  swifter  in  mid- 
stream than  at  the  edges. 


WORK   OF  AVALANCHES   AXD   GLACIERS     155 


Because  the  glacier  moves  more  rapidly  in  the  centre 
than  at  the  sides  of  the  stream,  the  surface  is  scored  with 
cracks  and  chasms  called  crevasses.  These  are  roughl}- 
parallel  and  cross  the  glacier  in  lines  which,  in  many  iu- 
stances,  point  upstream.^  In  some  cases  the  crevasses  form 
gently  curving  parallel  lines  that  are  not  unlike  the  rip- 
ples in  a  river.  Ordinaril}-,  the  crevasse  is  narrow  and 
only  a  few  feet  deep ;  but  in  some  places  it  becomes  a 
chasm  fifty  or  sixty  feet  from  top  to  bottom.  Crevasses 
are  most  numerous  in  that  part  of  the  glacier  where  the 
slope  is  the  steepest ;  and,  in  general,  they  mark  what  in  a 
river  would  be  the  rapids.  The  velocity  of  tbf  c uncut 
varies.  On  a  gentle 
slope  it  may  not  be 
more  than  three  or  four 
inches  a  day ;  on  a 
steep  incline  it  may  be 
half  as  many  feet.  In 
summer,  when  the  tem- 
perature is  above  the 
freezing  point,  the  mo- 
tion is  much  swifter 
than  in  winter — in  some 
instances  twice  as  great. 

As  the  ice-stream 
makes  its  way  down  the 
ravine,  fragments  of 
rock  fall  from  the  con- 
fining banks  and  lodge 
at  the  edges.  In  time,  these  accumulate  until  they  form 
walls  of  considerable  regularity.  These  walls  constitute  the 
lateral  moraines  of  the  glacier.  If  two  or  more  glaciers 
flow  into  the  same  ravine,  the  moraines  on  the  sides  that 
join  xanite  to  form  a  medial  moraine.     In  some  instances 


CREVASSES   AND    .MOKAIM       '  1    -i   ALLY 
GLACIER,   WASHINGTON 


15G  PHYSICAL   GEOGRAPHY 

several  medial  moraines  may  be  seen  stretching  with  great 
regularit}^  for  a  long  distance. 

ToAvard  the  lower  end  of  the  glacier,  much  of  this  sort 
of  rock  waste  gets  to  the  bottom,  in  front  of  the  ice-stream. 
In  summer,  when  the  lower  end  of  the  glacier  melts  to  a 
considerable  distance  vip-stream,  the  rock  waste,  consisting 
mainly  of  large  bowlders,  is  strewn  along  the  bed.  But  in 
winter,  when  the  ice- front  again  advances,  the  scattered 
bowlders  are  pushed  forward,  forming  across  the  path  of 
the  glacier  the  long  windrow  of  rock  waste  that  constitutes 
the  terminal  moraine. 

The  moraines  of  a  glacier  are  one  of  its  most  interest- 
ing and  important  features.  Not  infrequently  the  shape 
of  the  ravine  is  such  that  the  rocks  comjDOsing  the  lateral 
moraine  are  pushed  against  the  sides,  forming  walls  as 
regular  as  though  they  had  been  laid  by  human  hands. 
Moreover,  while  the  lateral  moraines  may  decrease  in  size, 
the  terminal  moraine  is  constantly  growing  in  volume. 

Glacial  Ice  Sheets. — Glacial  movements  are  not  con- 
fined to  the  ice  streams  of  ravines,  however.  The  sheet  of 
snow  that  projects  over  the  edge  of  a  roof  is  a  perfect 
illustration  of  glacier  motion ;  and  so,  too,  is  the  patch  of 
snow  on  a  steep  hillside  that  gradually  creeps  downward 
or  acquires  a  distorted  shape. 

But  there  are  remarkable  fields  of  ice  many  miles  in 
extent,  that  exhibit  all  the  phenomena  of  glacier  move- 
ment. These  vast  fields  are  found  mainly  in  polar  regions. 
They  are  not  confined  between  the  sides  of  ravines ;  they 
are  ice  sheets  of  vast  extent.  Probably  the  greater  part 
of  the  sheet  is  gradually  settling  downward ;  certainly  the 
ice  in  many  places  is  projecting  beyond  the  edges  and 
breaking  off. 

The  Greenland  ice  sheet  is  a  striking  example.  To  the 
best  of  our  knowledge,  almost  the  entire  island  is  covered 


WORK   OF   AVALANCHES   AND   GLACIERS     157 

with  ice  and  snow  that  have  been  accumulatinc::  during: 
long  periods  of  time.  So  far  as  kuoAvn  the  only  rock 
that  reaches  above  the  surface  of  the  ice  is  found  near 
the  coast,  where  the  ice-covering  is  thinnest. 

Along  the  southern  coast  much  of  the  ice  and  snow  dis- 
appears by  melting.  Farther  north,  however,  the  ice 
reaches  the  coast — sometimes  descending  into  the  fjords, 
sometimes  presenting  an  unbroken  wall  from  five  to  fifty 
miles  in  extent.     In  places  the  flow  of  the  ice  is  compara- 


l;IK"Hl    OF    TUB    IChl'.ERG 
Tlic  buoyant  force  of  the  water  ts    shearing  the  fragments,  and  the  latter  float  away. 


tively  rapid — as  much  as  forty  or  fift}'  feet  a  day.  The  frag- 
ments broken  from  the  ice  front  are  icebergs.  Sometimes 
they  tumble  from  the  to]) ;  in  other  instances  the  edge  of 
the  sheet  is  pushed  out  so  far  that  the  buoyant  force  of  the 
water  breaks  a  fragment  from  the  sheet,  and  it  floats  off". 

Huml)oldt  Glacier,  on  the  west  coast  of  Greenland,  is  a 
strikiug  cxann)le  of  the  ice-sheet.  For  a  distance  of  alxmt 
sixty  miles,  its  ragged  front,  broken  here  and  there  by 
rock-cliffs,  forms  a  sea-wall  in  ])laces  several  hundred  feet 


158  PHYSICAL   GEOGRAPHY 

high.  By  far  the  most  stupeudous  examples,  however, 
are  those  of  antarctic  regions.  Apparently  the  ice-sheet 
is  continental  in  size  and,  judging  from  the  thickness  of 
the  icebergs,  it  is  probably  several  miles  thick. 

Occurrence  of  Glaciers. —In  general,  glaciers  begin 
above  the  line  of  perpetual  snow  and  extend  usually  a 
short  distance  below  it.  In  high  latitudes,  where  the 
weather  is  cold,  they  occur  at  no  great  altitude  above  sea- 
level,  but  the  nearer  they  are  to  tropical  regions,  the 
higher  the  altitude.  In  low  latitudes  they  rarely  occur 
below  the  altitude  of  fifteen  thousand  feet,  while  in  polar 
regions  they  usually  flow  into<the  sea.  ' 

The  largest  stream  or  ravine  glaciers  known  are  in  the 
Himalaya  Mountains;  the  best  known  are  those  of  the 
Alps.  Along  the  northern  coast  of  Norway  there  are  fine 
examples ;  in  the  Patagonian  Andes,  and  along  the 
Alaskan  coast,  almost  every  arm  of  the  sea  contains  one  or 
more  of  them.  Study  the  character  of  these  coasts  on  a 
good  map.  In  the  Rocky  Mountains  there  are  numerous 
glaciers,  but  none  of  them  is  of  great  size.  Several  of  the 
glaciers  of  Mounts  Shasta  and  Tacoma  (Rainier)  rival  the 
Alpine  ice-streams  in  extent.  Muir  Glacier,  Alaska,  has 
a  frontage  of  two  miles  on  the  sea. 

Most  of  the  rivers  flowing  from  the  high  slopes  of 
mountains  that  reacli  above  the  snow-line  have  their  sources 
in  glaciers.     Find  examj^les  in  the  Alps. 

Physiographic  Effects  of  Glaciers. — The  results  of 
glacial  action  are  readily  observed  in  the  glaciers  of  the 
present  time  and,  indeed,  they  are  so  full  of  character  that 
they  are  a  most  excellent  key  Avhereby  the  stupendous 
effects  of  the  glaciers  of  prior  geological  times  have  been 
studied. 

The  chief  efi'ects  of  glacial  action  are  erosion  and  trans- 
portation.    Ice    alone    is  so  soft  that    it  has  little  or  no 


WORK    OF   AVALANCHES   AND    GLACIERS     159 

wearing  effect  on  hard  rock,  but  if  a  moving  mass  of  ice 
drags  or  pushes  fragments  of  rock  along  at  the  sides  and 
bottom  it  becomes  a  cutting  tool  of  great  power.  It 
planes,  gouges,  or  scratches,  according  to  the  character  of 
the  rock  over  which  it  moves. 

All  through  the  northern  United  States  and  Canada, 
nearly  to  the  Eocky  Mountains,  the  surface  has  been 
scoured  by  glacial  ice,  and  many  thousand  lake    basins 


REGION   OF   GLACIATION    IN    THK   UNITED   STATES 

The  heavy  tine  shows  the  limit  of  terminal  moraines  ■    erratie  boxvlders  occur  in  occasional 
localities  a  little  farther  south  of  the  line. 

have  been  made  or  shaped.  In  the  exposed  rock  of  New 
England  and  New  York,  the  grooved  and  rounded  surfaces 
are  one  of  the  most  marked  filatures,  and  ever^'Avhere  the 
erosion  is  so  characteristic  as  to  reveal  its  origin.  The 
northern  Appalachian  Mountains  were  worn  and  broken, 
and  the  wide  gaj)  between  the  Adirondack  and  Catskill 
ranges — both  groups  being  parts  of  the  Appalachian  folds 
— was  })robably  nwuh;  at  this  tinu;.     What  lias  been   the 


160 


PHYSICAL   GEOGRAPHY 


eliect  of  this  gap  on  the  commercial  development  of  New 
York?  That  the  surface  of  the  ice-sheet  did  not  reach 
quite  to  the  top  of  the  highest  peaks  of  the  Adirondack 
and  White  Mountains  is  inferred  from  the  fact  that  certain 
alpine  species  are  still  found  at  their  summits  that  do  not 
occur  at  a  lower  level. 

The  same  markings  are  equally  plain  throughout  north- 
ern Europe,  and  the  coasts  of  Norway  and  the  British 
Isles  probably  received  their  present  frayed  and  ragged 
appearance  at  the  same  time  that  so  much  of  North 
Amercia  was  covered  with  glacial  ice. 


A  DRUMLIN 
III  many  instances  the  surface  is  covered  with  fertile  soil. 

The  transportation  of  material  is  a  still  more  noticeable 
effect  of  glaciation,  and  the  rock  waste  that  has  been 
removed,  is  commonly  known  as  drift.  Glacial  drift  is 
unsorted  material,  and  in  size  the  pieces  vary  from  grains 
of  sand  to  bowlders  weighing  several  thousand  tons.  In 
character,  the  gravel  of  drift  differs  materially  from  stream 
gravel ;  for  while  the  latter  is  composed  of  uniformly 
rounded  pieces  the  fragments  of  the  former  are  rough  and 
angular,  with  one  or  more  faces  planed  smooth. 

Glacial  rock  waste  or  detritus  has  been  deposited  in 
various  forms.     Much  of  it  has  been  spread  over  the  sur- 


WORK  OF   AVALANCHES   AND    GLACIERS     IGl 


face  as  an  imperfectly  mixed  mass  of  clay,  sand,  and  gi'avel. 
These  deposits  are  the  well-known  till  plains  of  northern 
Europe  and  the  United  States.  Not  infrequently  the 
material  occurs  in  rounded  hillocks  or  drumlins,  or  per- 
haps in  loug 
ridge  -shaped 
bars,  called 
eskers.  The 
former  are  very 
common  in  the 
New  England 
Plateau,  th<' 
northern  lakt 
region,  and 
also  in  Eng- 
land and  Scot- 
land. Se¥eral 
of  the  islands 
in  Boston  har- 
bor are  drum- 
lins. 

Near  t  hu 
southern  limit 
of  the  glacial 
ice -sheet  the 
drift  occasion- 
ally takos  the 
form  of  long 
ridges— perha])s  many  miles  in  extent,  and  one  hundred 
feet  or  more  in  height.  In  nearly  every  instance  these 
heaps  are  moraines.  A  part  of  Long  Island  is  probably 
a  terminal  moraine,  and  several  of  the  ridges  that  cross 
New  Jersey  are  of  similar  origin.  Many  of  the  low  ridges 
extending  into  the  valleys  of  Colorado  are  moraines. 


bl'LlT    ROCK  ;    AN    KRRATIC    BOWLDUR 
Tin-  bitltenittl-tn'c,  growing  from  the  cliff,  is  forty  ytars  old. 


103  PHYSICAL   GEOGRAPHY 

A  remarkable  form  of  drift  is  found  in  the  romided 
blocks  of  stone  strewn  over  the  svirface  of  the  New  England 
and  Middle  Atlantic  States  and  a  few  other  localities. 
These  are  commonly  known  as  erratic  boivlders.  With  re- 
spect to  mineral  character  the  bowlders  are  of  many  kinds; 
those  of  the  northeastern  United  States  are  mainly  of 
granite.  The  most  interesting  feature  about  them  is 
the  fact  that  they  are  unhke  the  rock  in  the  locality 
where  they  are  found ;  in  some  instances  they  certainly 
have  been  brought  from  a  long  distance.  Some  of  them 
are  of  enormous  size  ;  one,  Split  Eock,'"  near  Mount  Ver- 
non, New  York,  weighs  not  far  from  five  hundred  tons. 

Icebergs. — The  formation  of  icebergs  along  the  sea- 
front  of  glaciers  becomes  an  important  factor  in  several 
ways.  The  icebergs  from  the  west  coast  of  Greenland  float 
southward  during  late  spring,  and  during  May  and  June 
cross  the  routes  of  trans-atlantic  steamships,  thus  becom- 
ing a  menace  to  navigation.  Sometimes  several  hundred 
of  them  are  drifting  about  in  the  vicinity  of  the  New- 
foundland Banks,  and  remain  there  until  they  melt  or  are 
broken  up  by  storms.  The  huge  blocks  broken  from  the 
Antarctic  ice-sheet  drift  about  over  a  very  large  area,  some- 
times being  found  as  far  north  as  latitude  40°  S.  In  the 
North  Pacific  Ocean  the  icebergs  are  small  and  are  rarely 
foiind  beyond  the  partly  enclosed  waters  of  the  Alaskan 
coast  and  Bering  Sea. 

QUESTIONS  AND  EXERCISES.— Describe  any  effects  you  have 
noticed  with  relation  to  snowslides  on  the  roofs  of  buildings  or  steep 
slopes. 

A  mass  of  snow  weighing  ten  thousand  tons  moves  with  a  velocity 
of  twenty-five  feet  per  second ;  what  is  its  momentum  in  foot- 
pounds ?  Would  this  force  be  sufficient  to  break  off  or  uproot  large 
trees  ? 

In  a  previous  paragraph  it  is  stated  that  the  water  issuing  from  the 
end  of  a  glacier  is  muddy  ;  account  for  the  presence  of  the  mud. 


WORK   OF   AVALANCHES   AND    GLACIERS     163 

Explain  the  way  in  which  rock  fragments  may  get  to  the  bottom  of  a 
glacier.     Why  are  the  scratches  made  by  these  fragments  parallel  ? 

Why  are  there  no  glaciers  in  the  Appalachian  Mountains  ? 

The  map  on  p.  157  shows  the  terminal  moraine  of  the  great  ice-sheet ; 
describe  its  course  and  location.  Name  two  large  lakes  situated  in  the 
basin  of  former  Lake  Agassiz. 

Describe  any  evidence  of  glaciation  in  the  neighborhood  in  which  you 
live,  noting  drumlins,  eskers,  moraines,  markings  and  scratches,  erratic 
bowlders,  or  drift.     If  possible  delineate  them  on  a  map. 

COLLATERAL   READING   AND   REFERENCE. 

Tyndall. — Foruiis  of  Water. 

Tyndall. — Hours  of  Exercise  in  the  Alps. 

Le  Coxte. — Elements  of  Geology,  pp.  569-583. 

NOTES 

'  It  is  rare  that  snow  accumulates  to  a  depth  of  more  than  ten 
or  twelve  feet  on  a  level  area.  On  mountain  slopes  the  snow  is 
not  evenly  distributed,  most  of  it  finally  lodging  in  ravines  and 
places  not  exposed  to  the  sweep  of  the  wind.  In  laying  the  foun- 
dations for  the  observatory  at  the  summit  of  Mont  Blanc,  the 
snow  and  ice  were  so  deep  that  no  rock  bottom  could  be  found  at 
a  depth  of  sixty  feet.  On  the  western  slope  of  the  Sierra  Nevada 
Mountains  the  fall  of  snow  sometimes  reaches  twenty  feet  on 
the  level,  while  the  drift  may  be  several  times  as  great. 

''  Wet  clothing  hung  out  to  dry  in  very  cold  weather  first 
freezes  and  then  gradually  dries.  An  inspection  of  Table  III., 
Appendix,  shows  that  at  a  temperature  of  —40°  F.  a  small  amount 
of  moisture  may  still  exist  in  the  atmosphere. 

'  The  power  of  wind  in  drifting  loose  .soil  has  already  been 
noted.  But  snow  is  less  than  one-cjuarter  as  heavy  as  soil  of 
average  material  ;  hence  the  work  oi  wind  is  far  more  effective. 

*  In  certain  parts  of  the  Rocky,  Cascade,  and  Sierra  Nevada 
Mountains  avalanches  are  of  frequent  occurrence,  but  they  are 
by  no  means  so  common  as  in  the  Alps.  In  the  latter  ranges  the 
slopes  are  steeper  and  the  snowfall  is  considerably  greater.  It  is 
not  improbable  that  such  snow-slides  are  just  as  conniion  and 
(juite  as  destructive  in  the  Caucasus  and  the  Himalaya  Moun- 
tains as  they  are  in  the  A!i)s. 


104  PHYSICAL   GEOGRAPHY 

'•  These  are  the  poudreuses  (powdery  snow),  and  they  are  the 
iin)st  dreaded  of  all  snowslides.  Damp  snow  does  not  shear  and 
move  readily  ;  it  is  tlie  gathering  ot  light,  dry  snow,  little  by 
little,  until  iinally  the  whole  mass  is  in  motion,  that  is  the  dis- 
tinctive feature  of  this  form  of  avalanche. 

"  This  form  is  known  as  the  avalanche  de  fond.  It  is  rarely 
destructive. 

'  The  bands  are  alternate  layers  of  ice  and  dirty  snow.  The  ice 
is  formed  of  snow  that  has  been  subjected  to  great  pressure.  Be- 
cause of  the  pressure  all  the  air  has  been  squeezed  out,  and  for 
this  reason  the  ice  is  tolerably  clear  and  blue.  The  bands  of  snow 
contain  air  and  are  therefore  whitish  and  opaque. 

"  The  *ice  hummocks  are  conical  in  shape  and,  if  present,  are 
found  almost  always  at  the  lower  end.  Not  infrequently  one  of 
these  hummocks  is  surmounted  by  a  bowlder  of  several  tons 
weight.  The  bowlder  protects  its  support  from  the  heat  of  the 
sun,  while  the  latter  melts  the  ice  around  the  lower  end  of  the 
column.  Sooner  or  later  the  iee  column  breaks  and  the  bowlder 
falls  to  a  lower  level,  where  the  same  process  is  again  repeated. 

"  This  peculiar  feature  at  one  time  gave  rise  to  the  opinion  that 
there  might  be  an  up-stream  motion  to  a  glacier.  The  reason  for 
their  direction,  however,  is  evident ;  the  crack  or  break  is  neces- 
sarily at  right  angles  to  the  direction  of  the  strain.  Now  the 
movement  of  the  ice  is  twofold — down  stream  and  away  from  the 
bank.  Therefore  when  the  ice  breaks  the  crack  points  diagonally 
up  the  stream. 

'"  Many  years  since  this  bowlder  broke  into  two  parts  along  a 
cleavage  plane.  A  butternut-tree  sprang  up  in  the  cleft  and  in 
time  its  trunk  has  wedged  the  two  fragments  apart  in  the  form 
of  a  V-shaped  opening.  In  the  northern  part  of  Westchester 
County  a  large  erratic  block  has  been  deposited  on  the  top  of 
three  smaller  stones,  the  latter  forming  a  very  firm  tripod.  In  a 
number  of  instances  one  bowlder  has  been  deposited  on  the  top 
of  a  boss  of  rock  in  such  a  position  that  the  equilibx'ium,  while 
more  or  less  unstable,  cannot  be  readily  overthrown.  Examples 
are  found  throughout  the  New  England  States,  and  they  are  pop- 
ularly known  as  rocking  stones.  There  is  a  fine  example  in 
Bronx  Park,  New  York  City.  Rocking  stones  are  also  common 
in  the  glaciated  regions  of  northern  Europe. 


CHAPTEE  X 

THE     WASTING    OF     THE     LAND  :      THE    EESULTS    OF 

IMPERFECT  AND  OBSTRUCTED  DRAINAGE.     LAKES 

AND  MARSHES 

In  floAving  from  higher  to  lower  levels  along  lines  of 
least  resistance,  the  water  may  find  its  passage  temporarily 
obstructed,  or  perhaps  wholly  blocked  by  obstacles. 
Sometimes  a  ridge  of  land  prevents  its  progress  ;  in  other 
cases  a  landslide  or,  perhaps,  a  stream  of  lava  athwart 
the  channel  prevents  its  progress.  The  water  therefore 
spreads  out,  forming  a  hike^  j^^nd,  or  marsh.  In  places 
where  the  flow  is  obstructed,  one  of  two  things  must  occur 
— either  the  water  will  collect  until  its  surface  is  high 
enough  to  flow  over  the  lowest  part  of  the  rim,  or  else  it 
will  spread  over  the  surface  until  the  amount  that  evapo- 
rates just  equals  that  which  Hows  in.  The  area  whose 
waters  flow  into  the  lake  constitutes  its  basin.  A  large 
basin  usually  has  several  rivers  and  many  small  streams 
that  are  its  tributaries  or  feeders. 

Marsh  Lakes. — In  a  region  of  considerable  rain-fall,  if 
the  general  slope  be  very  decided,  perliai)s  there  may  be  no 
lakes  and  ponds,  for  the  reason  that  the  water  flows  off, 
meeting  no  obstructions  which  cause  it  to  collect  in  basins.^ 
On  the  contrary,  if  the  surface  be  flat,  the  water,  finding 
no  definite  channels,  spreads  over  the  surface  and  forms  a 
multitude  of  small  ponds.  In  Florida  and  along  the  Gulf 
Coast  there  are  excellent  examples,  and  they  arc  commonly 
called  marsh  lakes.'^ 

165 


166 


PHYSICAL   GEOGRAPHY 


A  marsh  lake  of  large  size  or  considerable  depth  could 
not  form  in  perfectly  flat  lands,  for  the  reason  that,  after 
reaching  a  certain  height,  the  water  would  flow  ofl"  as  fast 
as  it  was  supplied.  For  a  similar  reason,  such  lakes  could 
not  be  very  luunerous  on  a  surface  that  had  a  consider- 
able slope/  But  while  many — perhaps  most — of  the 
lakes  have  been  formed  by  the  surplus  of  raiufall  over 
drainage,  there  are  many  thousand  lakes  that  are  the 
result  of  factors  with  which  rain-fall  has  no  direct  con- 


MARSH    LAKES,    FLORIDA. 


nection.  The  most  important  are  those  whose  basins  have 
been  shaped  largely  by  the  action  of  moving  streams  of 
ice — that  is,  by  glaciers. 

Glacial  Lakes. — A  glance  at  a  good  map  of  the  north- 
ern part  of  North  America  shows  that  the  lakes  of  this 
region  are  its  most  remarkable  surface  feature.  As  a  rule 
they  are  long  and  narrow,  and  if  a  group  of  them  be  con- 
sidered, it  is  at  once  apparent  that  their  axes,  or  lines  of 
greatest  length,  are  nearly  parallel.     Careful  investigations 


IMPERFECT  AND   OBSTRUCTED  DRAINAGE     167 

Lave  sliowu  that  not  only  are  such  hikes  comparatively 
much  deeper  than  the  marsh  lakes  previously  described, 
but  that  also,  iu  most  instances,  their  basins  have  been 
wrought  in  the  hardest  rocks.  In  many  instances,  too, 
their  rims  are  -walls  of  bowlders  that  could  scarcely  have 
been  more  regular,  had  the  courses  of  rock  been  laid  by 
human  hands.^ 

Very  frequently  such  lakes  occur  in  chains,  a  river  fol- 
lowing the  course  of  each  chain  ;  indeed,  these  lakes  are 


GLACIAL   LAKtS 
A  group  ill  the  AJiroiiiiack  Mountains,  New    York. 

merely  incidents  in  tlie  history  of  the  river.  In  a  few 
instances  a  cluster  of  such  lakes  apparently  radiates  from 
a  central  point,  as  is  seen  in  the  "linger"  lakes  of  New 
York.  Lakes  of  this  type  are  closely  associated  with  the 
great  accumulation  of  glacial  ice'^'  that  formerly  covered  a 
large  part  of  tlie  nortlioin  hemisphere.  The  lakes  them- 
selves are  found  in  glaciated  regions  only — never  else- 
where. They  are  therefore  called  glacial  lakes  or,  in  the 
British  Isles,  tains. 


1G8 


PHYSICAL   GEOGRAPHY 


Accidental  Lakes. — There  are  other  lakes  whose 
origin  is  the  result  of  accident ;  such  as  the  destruction 
of  a  river  loop,  the  damming  of  a  stream,^  the  formation 
of  a  bar  across  an  estuary  or  cove,  or  the  sinking  of  an 
area  of  land.  Very  many  lakes  have  come  suddenly  into 
existence  through  one  or  another  of  the  causes  named. 

In  the  illustrations  pp.  108  and  110  there  is  shown  a 
type  of  lake  that  is  common  along  tlie  bottom  lands  of  the 
Mississippi  and  other  rivers  that  flow  through  level  plains. 
The  origin  of  such  lakes  is  very  apparent.  The  lakes 
themselves  are  manifestly  the  abandoned  loops  of  rivers, 
and  they  are  formed  when  the  river  straightens  its  channel. 
The  Dwat  thus  formed  remains  filled  with  Avater.  Perhaps 
a  bayou  or  small  stream  may  be  left  as  a  feeder,  but  more 
likely  the  moat  becomes  a  stagnant  pool,  sooner  or  later 
to  disappear — possibly  overgrown  by  vegetation,  possibly 
buried  under  the  sediment  brought  down  by  floods. 

Another  type  of  accidental  lake  occurs  along  low,  flat 
coasts.     These  are  the  lagoons  of  the  sea-shore  or  the  lake- 

shore.  The 
south  coast  of 
Marthas  Vine- 
yard furnishes 
an  excellent  il- 
lustration of  la- 
goons of  this 
type.  In  times 
past,  this  shore 
was  a  succes- 
sion of  coves 
and  small  bays. 
But  the  water 
on  this  side  of  the  island  is  so  shallow  that  the  waves, 
dragging  heavily  on  the  bottom,  have  pushed  enough  sand 


LAGOONS,    MARTHAS   VINEYARD 


IMPERFECT  AND   OBSTRUCTED   DRAINAGE     169 

before  theui  to  throw  barriers  across  the  coves,  and  shut 
them  off  from  the  oceau.** 

Any  good  map  of  the  United  States  or  of  Europe  will 
show  a  multitude  of  Avave-formed  lagoons  of  this  character. 
Those  near  the  shore  often  have  more  the  nature  of  sounds 
than  of  lagoons.^  But  as  the  coast,  little  by  little,  extends 
seaward,  many  of  them  now  near  the  shore  Avill  ulti- 
mately be  at  a  considerable  distance  inland. 

Salt  Lakes. — Salt  lakes  have  no  outlets,  and  for  that 
reason  they  are  salt.''^  Nearly  all  soil  contains  more  or 
less  mineral  salts  that  are  soluble  in  water.  Even  the 
hardest  granites  and  igneous  rocks  contain  a  minute  pro- 
jKjrtion  of  soluble  matter.  So  when  the  water  flows  to 
the  basin,  it  carries  with  it  any  soluble  matter  with  which 
it  comes  in  contact.  If  the  lake  or  pond  has  an  outlet, 
l)otli  the  water  and  the  salt  flow  ofi"  together."  If  there 
be  no  outlet,  however,  the  water  is  removed  by  evapora- 
tion, while  the  mineral  salts,  Avliich  cannot  evaporate, 
remain  in  the  basin.  In  time,  the  water  becomes  decid- 
edly salt,  and  finally,  a  brine  that  will  dissolve  nothing 
more.  After  this,  unless  there  is  an  inflow  of  fresh  water, 
the  salt  sinks  to  the  bottom,  and  forms  also  a  wide  mar- 
gin of  crusted  salt  along  the  shore. 

Temperature  and  atmospheric  moisture  are  also  factors 
in  the  origin  of  salt  lakes.  High  temperature  and  dry- 
ness of  the  atmosphere  both  promote  evaporation,  and 
doubtless  there  are  regions,  whose  lakes  are  now  fresh, 
that  would  become  regions  of  salt  lakes  were  the  tem- 
perature and  dryness  to  increase  materially. 

Although  salt  lakes  have  no  outlets,  it  is  not  necessarily 
true  that  lakes  without  outlets  are  salt.  As  a  matter  of 
fact,  there  are  many  such  lakes  whose  waters  are  almost 
as  sweet  and  pure  as  when  they  fell  from  the  clouds.  Of 
this  apparent  contradiction  there  are  two  explanations. 


170  PHYSICAL   CxEOGRAPHY 

111  the  first  place  the  lakes  may  be  young.  In  this  case, 
time  only  is  required  to  cliauf^e  the  fresh  lake  to  one  of 
brine,  and  the  time  will  be  long  or  short,  according  as 
the  soil  through  which  the  feeders  flow  contains  little  or 
much  soluble  matter.  In  the  Great  Basin,  Avest  of  the 
Kocky  IMountains,  there  are  several  young  lakes,  whose 
waters  are  comparatively  fresh,^'  situated  almost  alongside 
lakes  of  briny  saltness.  In  the  second  place,  all  the 
soluble  matter  may  have  been  leached  from  the  soil  at 
some  prior  time  when  the  lake  overflowed  its  basin. 
There  are  many  such  lakes  in  Canada  and  the  United 
States.  They  are  not  salt,  and  unless  their  conditions  of 
existence  are  changed  they  will  not  become  salt. 

There  are  certain  lakes,  mainly  in  arid  regions,  that  are 
periodic  in  character.  During  the  rainy  season  they  may 
be  of  considerable  size  ;  they  have  no  great  depth,  how- 
ever, and  in  the  dry  season  their  waters  evaporate,  leaving 
in  each  basin  a  thick  crust  of  salt.  There  are  numerous 
small  lakes  of  this  character  in  the  western  part  of  the 
United  States;  some  of  those  in  southern  Russia  are  of 
considerable  area.  Lakes  of  this  kind  are  commonly  called 
playa  lakes.  Commercially  some  of  them  are  important 
on  account  of  the  enormous  amount  of  salt  they  yield. 

Physiographic  Aspect  of  Lakes.— Lakes  are  the  most 
transitory  features  of  the  earth's  surface.  Rivers  and  the 
various  relief  features  of  the  earth  are  seldom  entirely 
obliterated ;  but  as  time  is  reckoned  a  lake  is  the  creation 
of  a  very  brief  period.  Its  life  is  almost  ephemeral,  and 
various  forces  are  constantly  at  w^ork  to  destroy  it.  Physi- 
ographic agents  that  have  no  effect  on  other  features  of 
the  earth  are  often  fatal  to  the  existence  of  lakes. 

Among  the  various  agents,  glaciers  are,  perhaps,  the 
chief.  Glaciers  have  been  energetic  factors  in  making 
lakes,  it  is  true ;  they  have  also  been  quite  as  effective  in 


IMPERFECT  AXD  OBSTRUCTED  DRAINAGE     171 

causing  their  destructiou.  The  glacier  blocks  the  channel 
of  a  river  with  ice  or  with  gravel,  and  in  a  short  time  a  lake 
is  formed.  Later  it  forces  a  passage  through  the  obstruc- 
tions made,  and  in  a  little  while  the  lake  has  disappeared.'" 
A  few  old  shore  marks  and,  perhaps,  a  delta  or  two  are  all 
that  remain  to  tell  the  storv. 


A   BURIED   LAKE   BASIN 
TItc  basin  has  been  filled  with  sediments  brought  into  it  by  the  river. 


A  change  in  the  level  of  the  lake-bed  by  elevation  or  by 
depression  always  produces  great  changes  in  the  lake.  Such 
a  change  may  throw  up  a  ridge  so  as  to  form  a  basin  for  a 
new  lake,  })ut  it  may  also  lowcn*  the  land  at  the  foot  of  the 
lake  and  destroy  the  basin  of  an  old  one.  Long  before  the 
existence  of  the  lakes  whose  remnants  are  now  found  in 
the  Great    Basit),  a  vast  bodv  of  water  covered  nmch  of 


172  PHYSICAL   GEOGRAPHY 

this  region.  But  a  change  in  the  level  of  the  basin 
occurred,  and  this,  together  with  probable  changes  in 
climate,  caused  the  great  internal  seas  gradually  to  dis- 
appear.'^ 

llapidly  growing  vegetation  is  also  a  potent  factor  in 
the  destruction  of  lakes.  Vegetation  has  but  little  effect 
on  deep  lakes,  but  in  the  case  of  marsh  lakes  it  has  a  great 
deal.  The  process  is  very  simple  :  the  roots,  stalks,  and 
leaves  of  the  dead  j^lants  fill  the  basin  until  there  is  no 
more  room  for  the  lodgement  of  water.  Usually  the  plant 
begins  its  growth  at  the  edge  of  the  lake  and  spreads 
toward  the  centre,  gradually  filling  the  basin,  until  a  deep 
hole  is  all  that  remains.  The  struggle  of  the  lake  may  lie 
a  long  one,  biitin  the  end  the  vegetation  conquers.  Buried 
and  partly  obliterated  lakes  of  this  character  are  common 
in  all  coast  plains  and  level  lands.  One  near  Goshen, 
New  York,  covering  an  area  of  about  sixty  square  miles, 
has  disappeared  within  recent  times  and  most  of  its  former 
bed  is  now  cultivated  land — the  famous  "onion  fields"  of 
the  State. 

Winds  are  sometimes  very  effective  in  the  destruction 
of  lakes,  especially  the  lagoons  along  the  seashore.  The 
manner  in  which  they  operate  is  very  simple  ;  they  merely 
carry  enoiigh  fine  rock  waste  into  the  basin  to  fill  it.'^ 
The  rock  waste  is  piled  upon  the  M-indward  shore,  and 
the  latter  advances,  little  by  little,  until  finally  it  meets 
the  opposite  shore.  The  lagoon  is  filled,  and  at  tlie 
same  time  an  estuary  becomes  a  j^art  of  the  coast  plain. 
Such  instances  are  common  on  coasts  that  are  swept  by 
constant  winds. 

The  foregoing  are  the  most  apparent  agencies  that  con- 
tribute to  the  destruction  of  lakes  ;  and  although  in  many 
instances  they  operate  continuously  and  systematically, 
they  are  confined  to  localities  of  comparatively  small  area. 


IMPERFECT  AXD  OBSTRUCTED  DRAINAGE     173 


But  there  are  other  lake-destroying  agencies  whose  opera- 
tions are  carried  on  in  ahnost  every  part  of  the  earth ; 
their  manner  may  not  be  quite  so  apparent,  but  it  is  none 
the  less  efiective.  "  Rivers  are  the  mortal  enemies  of 
lakes."*  The  stream  that  flows  into  a  lake  bears  in  its 
volume  more  or  less  silt,  which  is  promptly  deposited  in 
the  lake  basin,  lit- 
tle by  little  filling 
it.  With  scarcely 
an  exception,  at 
the  place  where  a 
stream  enters  a 
lake,  either  a  del- 
ta or  a  bar  is 
formed.  This  is 
clearly  illustrated 
by  the  Volga,  with 
its  mazy  delta  ; 
by  the  St.  Louis, 
at  the  head  of 
Lake    Superior; 

and  by  St.  Clair  River,  at  the  head  of  Lake  St.  Clair,  and 
in  the  lakes  of  central  New  York. 

The  stream  that  flows  out  of  the  lake  is  equally  destruc- 
tive. It  cuts  away  the  rim  of  the  basin,  lowering  the  level 
of  the  lake  until  the  water  is  nearly  or  quite  drained.  Not 
a  few  of  the  lakes  that  have  disappeared  from  the  earth 
have  been  destroyed  in  this  manner. 

A  diminution  in  the  rainfall  sooner  or  later  will  also 
destroy  a  lake.  The  lakes  and  old  lake-beds  in  the  Clreat 
Basin  illustrate  this  fact.  Formerly  Great  Salt  Lake  and 
its  scattered  remnants — the  latter,  many  of  them,  now  dry 
— covered  an  area  almost  half  the  size  of  Lake  Superior. 

♦  Gill.ert. 


LAKE  ST.  CLAIR. 

The  mud  fiats  at  the  head  of  the  lake  are  the  remit  of  sedi- 
mentation. 


174 


PHYSICAL   GEOGRAPHY 


FnrnuT  Luke  I  I 

iJry  La  ml  |  | 


LAKE   BONNEVILLE   AND   ITS   REMNANTS 

The  area  in  white  shows  the  former  si^e  of  the  lake  ;  the  small 
lakes  south  of  Sevier  H^iver  are  practically  dry. 


At  that  time  the 
level  of  the  lake 
was  nearly  one 
thousand  feet 
higher  than  at 
present.  After- 
wards, however, 
the  rainfall  de- 
creased and,  the 
indraught  being 
less  than  the 
loss  by  evapor- 
ation, the  lake 
dwindled  to  its 
present  size. 

In  almost 
every  part  of 
the  Avorld  are 
found  old  lake 
shore-lines  high 
above  the  sur- 
face whose  level 
they  formerly 
marked."^  In 
some  instances 
they  surround 
the  sites  of 
lakes  that  have 
ceased  to  ex- 
ist ;  in  others, 
of  lakes  that  are 
reaching  a  j)e- 
riod  of  old  age. 
In    any    case 


IMPERFECT  AND  OBSTRUCTED  DRAINAGE    175 

they  serve  to  demonstrate  that  lakes  are  very  transit- 
ory. 

Many  of  the  lakes  of  the  United  States  have  disap- 
peared within  very  recent  times.  Sevier  Lake  in  Utah 
has  practically  ceased  to  exist,  and  Tulare  Lake,  California, 
in  twenty  years  has  shrunk  to  less  than  half  its  former 
size.  The  finger  lakes  of  New  York  have  lost  a  measur- 
able part  of  their  area  in  the  past  fifty  years,  and  the  level 
of  the  Great  Lakes  has  been  materially  lowered.  In  Lake 
Erie  the  diminution  has  interfered  so  much  with  navi- 
gation that  a  barrier  across  the  outlet  is  now  contem- 
plated in  order  to  raise  tli*^  level  of  the  lake. 

Geographical  Distribution  of  Lakes.— Lakes  occur 
in  all  parts  of  the  earth,  but  they  are  by  no  means  uni- 
formly distril)uted ;  as  a  matter  of  fact  about  ninety 
per  cent,  of  them  are  north  of  the  40th  parallel  of  north 
latitude. 

With  respect  to  glacial  lakes  this  law  holds  almost 
universally  true.  The  only  exceptions  are  the  few  that 
are  found  in  the  southern  Andes  and  the  snow-clad  sum- 
mits of  high  plateaus  and  mountains.  Most  of  them 
are  situated  in  Europe  and  North  America.  In  the  lat- 
ter division  alone  there  are  more  than  one  hundred 
thousand  glacial  lakes.  Why  are  the  latter  of  rare  occur- 
rence in  the  torrid  zone  ?  Where  in  this  zone  would  they 
occur  ? 

Salt  lakes  are  confined  mainly  to  regions  of  deficient 
rainfall.''  Why  are  thf^y  not  common  in  regions  of  abun- 
dant rainfall  ?  Most  of  them  occur  in  the  basin  regions  of 
North  America  and  Eurasia ;  in  the  latter  region  there  are 
several  thousand.  The  Caspian  "  Sea,"  the  largest  lake  in 
the  world,  is  in  this  region ;  its  surface  is  eighty-four  f('<;t 
below  sea-level.  Playa  lakes  are  numerous  in  regions 
having  a  level  surface  and  a  light,  periodic  rainfall. 


17(5 


PHYSICAL   GEOGRAPHY 


Most  of  the  lakes  may  be 
grouped    in    systems    which 
occupy   lines   of   depression 
on  the  earth's  surface.     Two 
such  systems  are  found  in 
the  Western  and  three  in  the 
Eastern   Continent,     The 
lakes  of  the  Western  Conti- 
nent   are    chiefly   in   North 
America,  and  are  embraced 
mainly  in  two  systems.    The 
largest  and  most  important 
is  the  belt  stretching  across 
the  northern  part  of  North 
America.     An  arc  of  a  great 
circle    drawn   from  the   city 
of  Buflalo  to  Point  Barrow 
passes    through    or   near    a 
chain  of  lakes  that  includes 
about  the  largest  bodies  of 
fresh   water    in    the   world. 
Find  this  chain  on  the  maj) ; 
describe   the    drainage    and 
character  of  the  lakes.     An- 
other system   extends   from 
the    northern    boundary    of 
the  United  States  southward 
through    Mexico    and    the 
Central  American    States. 
Most  of   these  are  situated 
in  a  basin  region ;  describe 
their  drainage  and  character. 
South  America  is  remark- 
able for  the  absence  of  lakes 


IMPERFECT  AND  OBSTRUCTED  DRAINAGE     177 

in  any  considerable  number.  There  are  playa  lakes  along 
the  eastern  base  of  the  Andes,  but  the  only  lake  of  impor- 
tance is  Titicaca/^  a  large  body  of  water  near  the  summit 
of  the  Andes.  Its  surface  is  13,000  feet  above  seadevel, 
and  it  is  the  highest  large  lake  in  the  world.  Do  its  waters 
reach  the  ocean  ? 

In  the  eastern  continent  a  wide  belt  of  lakes,  situated 
mainly  between  the  50th  and  60th  parallels,  extends  across 
Eurasia;  what  is  their  character?  With  resj)ect  to  lati- 
tude their  position  corresponds  pretty  closely  to  that  of 
the  glacial  lakes  of  North  America.  These  lakes  constitute 
the  great  majorit}-  in  number,  but  they  are  of  very  little 
importance. 

A  second  belt  follows  the  high  mountain-ranges  thas 
stretch  from  west  to  east  across  the  continent.  It  em 
braces  the  playa  lakes  south  of  the  Atlas  Mountains ;  the 
glacial  lake  of  the  Alpine  and  Himalayan  folds  ;  and  the 
multitude  of  playa  and  salt  lakes  in  the  basin  region. 
Many  of  the  largest  and  most  of  the  important  lakes  of  the 
continent  are  in  this  group.  A  third  system  in  Africa 
follows  the  line  of  the  eastern  highlands,  and  therefore, 
unlike  the  other  systems,  extends  north  and  south. 
JSext  to  those  of  North  America  the  African  lakes  are  the 
largest  bodies  of  fresh  water  in  the  world.  Name  and. de- 
scribe the  four  largest. 

In  one  respect  the  Australian  lakes  are  remarkable — 
almost  every  one  is  either  a  playa  or  a  salt  lake.  Not  a 
single  one  of  any  importance  has  an  outlet  to  the  sea. 
What  does  this  indicate  with  reference  to  the  rainfall  of 
tlie  continent  ? 

Swamps  and  Marshes. — In  some  places  the  drainage 
waters  cannot  ilow  otl',  l)ut  remain  about  even  with  the 
surface,  thereby  foiinijig  what  are  variously  termed 
siiyintps,  uiordsscs,  jinc<isoiis^  /">',/■'<,  '""^  iiKirsJics.^^ 


178  PUVSrOAL   GEOGRAPHY 

Inasmuch  as  almost  every  conditiou  of  imperfect  or 
embarrassed  drainage  results  in  marshy  ground,  it  is  evi- 
dent that  many  different  factors  may  bring  about  such 
conditions.  For  instance,  the  surface  of  the  laud  may  be 
so  nearly  a  perfect  level  that  the  water  cannot  run  off 
until  it  has  completely  saturated  the  soil.  Such  instances 
are  very  common  :  they  occur  in  prairies  and  the  flood 
plains  of  rivers  almost  without  number.  They  are  com- 
monly, though  not  always  properly,  called  7-iver  terrace 
swamps.  Quite  as  frequently  such  morasses  form  at  the 
mouths  of  rivers,  where  they  form  delta  siuamps,  or  estuary 
sivamps. 

In  many  instances  the  accumulation  of  vegetable  matter 
results  in  swamps.  Under  ordinary  conditions  the  leaves 
and  twigs  of  forest  growths  quickly  decay  if  they  fall  on 
dry  ground  and,  as  a  rule,  the  products  of  decay  are 
gaseous.  Under  such  circumstances,  therefore,  no  great 
amount  of  solid  matter  results  from  such  decay.  But  if 
the  ground  be  tolerably  wet  and  rainfalls  are  frequent, 
there  may  be  enough  moistiire  to  prevent  complete  decay. 
The  vegetable  matter  gradually  acquires  a  well-known 
condition,  in  which  it  consists  of  a  fine,  black  slime  and  a 
mass  of  fibrous  material  called  peat!^^  The  accumulated 
matter  prevents  drainage  and  a  swamp  finally  results. 
Most  looodland  sioamps  are  formed  in  this  way. 

Not  all  woodlands  become  swamps,  however,  for  the 
character  of  the  vegetation  nearly  always  has  more  or  less 
to  do  in  swamp-making.  Several  species  of  sphagnum,  a 
kind  of  moss,  are  intimately  connected  with  swamps.  One 
of  these  water-mosses  consists  of  very  long,  thread-like 
stems  which,  while  dead  at  one  end,  are  living  and  grow- 
ing at  the  other.  Tl)e  dead  portions  do  not  decay,  how- 
ever ;  they  simply  accumulate,  packing  tightly  together 
like  an  immense  mass  of  sponge. 


IMPERFECT  AND  OBSTRUCTED  DRAINAGE     179 

So,  if  the  ground  ever  becomes  wet  euougli  for  the 
water-loviug  sf)hagnum  to  get  possession,  the  area  will 
become  a  swamp,  even  if  the  accumulations  of  other  vege- 
table materitil  would  not  result  that  way.  In  time  a 
hollow,  a  pond,  or  even  a  marsh  lake  will  be  entirely  filled 


EFFECTS   OF   VEGETATION 
Su'nm/>  vegclation  beginning  at  the  ihoic,  are  exieiijiiig  oiilnutnls. 

with  the  stems  of  s})hagnum,  thus  forming  peat  Imh/s  and 
lacastrliie  swarupsr^ 

If  sphagnum  once  obtains  in  an  area,  an  absolutely 
level  surface  is  not  necessary  for  the  formation  of  swamps. 
The  sphagnum  will  make  its  way  up  a  slope  of  four  or 
five  degrees  and  thus  form  a  climbing  hog.  Instances  of 
this  kind  are  common  in  the  Scandinavian  Peuinsiila  and 
also  in  Nova  Scotia  and  the  New  England  States. 


xVv."«  '^f,->t^j^'^»'fv^'fi*v'^,''f''"''-)fir^'f'r^^\^^^^ 


EFFECTS  OF   VEGETATION 

Swamp  grasses  and  sphagnum  have  nearly  filled  the   lake,  and  a  quaking  hog  ts  beginning 

to  form. 

Sphagiious  growths  not  only  overwliclin  shallow  i)onds 
and  lakes,  by  filling  their  basins  from  top  to  bottom,  but 
som('tiiiie,s  they  o])erate  against  d('op(!r  waters.  If  the  moss 
stems  cannot  find  lodgement  at  the  bottom  of  the  lake  tlicy 
will  Hoat  at  the  surfacf^  spreading,  little  l)y  little,  initil  tlie 
surface  is  covered.     '^J'Ik;  mat  of  sphagnum   gi'ows   tliickei- 


180  PHYSICAL   GEOGRAPHY 

aud  bromler,  and  is  made  firmer  by  pasty  matter,  that 
results  from  partial  decomposition.  In  time  the  surface 
becomes  firm  enough  to  serve  as  the  bed  of  a  wagon  road, 
or  even  a  railway.  But  the  surface  never  gets  quite  firm, 
and  when  one  jumps  uj^on  it,  or  drives  a  wagon  over  it,  the 
shaking  is  always  perceptible.  In  this  manner  a  marsh 
lake  is  changed  to  a  quaking  hog^^  or  prairie  tremblanfe. 

There  are  other  species  of  vegetation  ''^^  that  have  more 
or  less  to  do  with  swamp  formation — among  them  cane- 
brakes.  Canebrakes  have  long  been  associated  with 
swamps,  but  usually  as  a  result.  As  a  matter  of  fact, 
canebrakes  are  not  infrequently  a  cause  of  swamps.  The 
roots  of  the  plant,  spread  out  just  below  the  surface  of  the 
ground  in  much  the  same  manner  as  does  the  sphagnum 
above  ground,  making  finally  a  mat  that  almost  wholly 
obstructs  drainage. 

Coast  or  salt  marshes  are  confined  to  low  coast  plains. 
They  are  destitute  of  water  mosses,  but  they  contain  other 
species  of  vegetation  that  are  quite  as  effective.  The  first 
step  in  the  formation  of  a  salt  marsh  is  an  area  of  shallow, 
still  water.  Usually  this  results  as  soon  as  a  sand-bar  is 
thrown  across  a  cove  or  estuary.  Waves  prevent  the 
development  of  marine  swamp,  but  in  throwing  up  a  bar 
they  make  the  condition  that  is  a  foundation  for  the 
swamp.  In  a  few  instances  sheltering  headlands  keep  the 
water  still  enough  for  the  growth  of  marine  plants. 

The  next  stage  is  the  growth  of  eel  grass,  a  plant  with  a 
long,  slender  blade.  This  takes  root  as  soon  as  the  cove 
begins  to  fill  with  sediment ;  it  grows  rapidly,  and  the 
half-decayed  remains  contribute  not  a  little  in  filling  up 
the  marsh.  But  eel  grass  grows  only  when  covered  with 
salt  water,  and  when  the  decayed  vegetation,  mixed  with 
wind-blown  rock  waste,  has  filled  the  cove  to  low-tide 
level,  it   perishes.     After  a  time  the  marsh  passes  a  step 


IMPERFECT  ANT)   OHSTRUCTED  DRAINAGE     181 

higher  iu  its  formatiou,  receiving  layer  after  layer  of  sedi- 
ment that  build  its  surface  to  a  level  Avliere  it  is  awash  at 
high  tide  only. 

By  this  time  true  salt-marsh  grasses,  reeds,  rushes,  and 
tules  obtain  possession.  These  species  thrive  only  when 
their  roots  are  covered  with  salt  water  at  short  intervals. 
They  accumulate  until  the  level  of  the  marsh  is  built 
above  the  level  of  the  highest  tides.  When  this  stage  is 
reached  turf  grasses  gradually  take  the  place  of  salt-marsh 
grasses,  and  the  marsh  becomes  meadow  land. 

Another  plant  active  in  swamp-making  is  the  mangrove- 
tree.  This  tree  thrives  only  iu  salt  water.  It  propagates 
itself  partly  by  upshoots  from  the  enormous  mass  of  roots 
that  trail  under  water,  and  partly  by  seeds.  The  growth 
and  spreading  of  mangrove  roots  and  trunks  is  so  great 
ohat  coast  outlines  are  extended  rapidly  and  fringing  bur- 
riers  are  formed  as  well.  In  Florida  mangroves  and  corals 
are  yearly  adding  measurably  to  the  swamp-land  surface 
of  the  State. 

The  tundras  of  the  Arctic  coast  plain  furnish  an  inter- 
esting example  of  the  combined  action  of  ice,  fresh  water, 
salt  water,  and  moss.  These  shores  are  almost  constantly 
covered  with  ice.  Not  only  are  they  inundated  by  tidal 
waters,  but  also  by  stream  waters.  The  mouths  of  the 
streams  are  frozen,  and  the  flood  water,  finding  its  chan- 
nels blocked  with  ice,  spreads  broadcast  over  the  surface. 

During  flood  seasons  the  stream  waters  are  tilled  with 
sediment,  and  this  is  spread  over  the  plain.  Moreover,  it 
furnishes  siifhcient  nutriment  to  heavy  growths  of  coarse 
moss,  and  the  latter,  in  turn,  not  only  holds  the  sediment 
in  place,  but  it  also  in  no  small  degree  prevents  the  melt- 
ing of  the  ice.  As  a  result,  this  plain  is  a  perpetually  half- 
frozen  morass,  and  probably  the  most  inhospitable  region 
on  the  face  of  the  earth. 


183  PHYSICAL   GEOGRAPHY 

Physiographic  Aspects  of  Marshes. — Notwithstand- 
ing the  fact  that  the  area  of  marshes  and  swamp  is  com- 
paratively small,  it  is  probable  that  much  of  the  land  sur- 
face of  the  earth  has  been  a  marsh  or  a  swamp  in  some 
period  of  its  existence.  In  a  way  marine  marshes  may  be 
considered  as  laud  at  an  intermediate  stage  between  sub- 
mergence and  elevation.  Hence,  volcanic  areas  excepted, 
the  shallow  lagoon,  the  eel  grass  swamp,  the  barren  mud 
flat,  the  salt  grass  marsh,  and  the  turf-covered  plain  is 
each,  in  turn,  an  incident  in  the  final  elevation  of  a  body  of 
land  above  sea-level. 

Along  the  coast  of  the  South  Atlantic  States  one  may 
find  the  lagoons  and  the  eel  grass  swamps  ;  along  the 
shores  of  the  Gulf  there  are,  in  addition,  very  broad  mud- 
flats;'^ in  the  bay  of  San  Francisco  and  the  adjacent 
waters  are  many  square  miles  of  salt-grass  and  tule 
marshes  ;  and  almost  everywhere  beyond  the  reach  of  tidal 
waters  there  are  the  turf- covered  plains. 

The  range  of  fresh-Avater  swamps  may  not  be  quite  so 
great,  but  economically  they  are  quite  as  important  as  the 
marine  marshes.  Their  evolution  and  physiography, 
moreover,  is  rather  more  complex  than  the  development 
of  marine  marshes,  but  in  two  respects  they  are  alike — ■ 
namely,  vegetation  makes  them  and,  in  the  long  run,  it  de- 
stroys them. 

Vegetation  may,  and  usually  does,  operate  to  create 
swampy  conditions,  but  the  process  of  destruction  does 
not  differ  from  that  of  creation.  The  accumulation  pro- 
ceeds until  the  surface  is  lifted  to  a  level  where  the  ground 
waters  may  flow  off. 

Cultivation  destroys  swamps,  and  the  process  of  destruc- 
tion is  simple.  Most  grains  and  food-stuffs  require  a  com- 
paratively dry  soil,  and  the  very  act  of  ploughing  creates 
draina«fe  channels  in  which  the  water  flows  off.     Where 


IMPERFECT  AND  OBSTRUCTED   DRAINAGE     183 

ploughing  lias  not  been  sufficient,  ditching  and  under- 
draining  accomplish  the  same  results. 

But  swamps  themselves  exert  not  a  little  influence  on 
vegetation  and  its  distribution.  Many  species  of  tree  and 
shrub  that  thrive  in  moist  or  dry  soils  perish  if  the  soil  be 
saturated.  Thus,  a  swamp  once  obtaining  in  a  woodland 
area,  it  is  a  question  of  time  only  before  many,  possibly 
all  of  the  forest  species  disappear.  In  almost  every  fresh- 
Avater  swamp  the  most  marked  features  are  the  stumps 
and  trunks  of  dead  trees — a  result  of  the  development  of 
swampy  conditions.  What  species  of  evergreen  thrives  in 
swampy  lands  ? 

Economic  Value  of  Swamps. — Sw^amp,  marshes,  and 
bogs,  although  practically  uninhabitable  for  human  beings, 
have  had  a  very  far-reaching  effect  in  the  development  of 
civilization.  In  evidence  of  this  the  results  of  the  coal-beds 
may  be  cited.  The  enormous  development  of  commerce 
and  manufactures  is  due  almost  wholly  to  the  coal-fields  of 
the  world,  and  these  almost  without  exception  are  the 
swamps  and  marshes  of  prior  geological  ages. 

The  swamps  of  the  present  time  are  the  most  productive 
areas  to  be  drawn  upon  in  the  future.  The  soil  possesses 
great  depth,  and  its  nutrient  qualities  are  exceedingly 
great.  Swampland  crops  themselves  are  of  no  little  im- 
portance, and  the  rice-swamps  probably  supply  food  to  a 
greater  number  of  people  than  all  the  other  grain-fields  in 
the  world.  Incidentally,  the  world's  supply  of  cranberries 
comes  mainly  from  swamps,  and  the  peat-bogs  furnish  fuel 
to  not  far  from  fifty  millions  of  people. 

The  Movement  of  Rock  Waste. — In  this  and  the 
preceding  chapters  it  has  been  shown  that  the  higher  parts 
of  the  land  are  almost  everywhere  crumbling  and  wasting 
away  under  the  action  of  water  in  one  or  another  of  its 
different  forms.     Rain,   snow,   ice,   running  streams,  and 


184  PHYSICAL   GEOGRAPHY 

even  the  winds  are  factors  that  are  unceasingly  active,  and 
their  legitimate  work  is  to  wear  away  the  land  and  trans- 
port the  material  rcniioved  to  sea-level. 

On  the  steeper  slopes,  as  a  rule,  the  rock  waste  is  coarse, 
the  fragments  sometimes  weighing  many  tons.  On  its 
way  downward  it  is  broken  and  worn  in  various  ways 
until,  at  sea-level,  it  is  very  fine.  Much  of  it  is  also  min- 
gled with  the  remains  of  vegetation,  and  takes  the  charac- 
ter called  soil. 

The  soil  is  deposited  in  river  valleys  in  the  form  of  flood 
plains,  delta  plains,  estuary  plains,  and  coast  plains.  Re- 
view briefly  the  formation  of  each.  Some  of  it  is  arrested 
by  obstructions  along  its  downward  journey  and,  filling  the 
depressions  in  front  of  the  barriers,  forms  lacustrine  plains. 
Name  several  examples.  Explain  how  all  these  physio- 
graphic processes  aflect  the  habitability  of  a  region. 

The  ivaste  of  the  old  land  is  the  material  of  the  new. 

QUESTIONS  AND  EXERCISES.— Study  any  lake  or  pond  near 
which  you  live  and  classify  it  as  marsh,  glacial,  swamp  hole,  or  salt ; 
make  a  map  of  it. 

Note  whether  a  coast  plain  is  present,  or  whether  the  water-level  is_ 
at  the  foot  of  cliffs  or  banks. 

If  there  is  a  fringe  or  belt  of  coast  plain  what  does  it  indicate  con- 
cerning the  present  and  the  former  size  of  the  lake  ? 

Note  whether  or  not  the  border  is  marshy  and  thickly  covered  with 
vegetation,  or  whether  it  is  strewn  with  large  bowlders. 

In  what,  if  any,  part  are  the  waters  muddy  ?  From  this  determina- 
tion endeavor  to  find  where  the  sediment  is  chiefly  deposited. 

From  the  foregoing  write  a  description  of  the  body  of  water. 

From  the  diagram  of  the  Great  Lakes,  together  with  a  good  map, 
p.  176,  prepare  a  description  of  these  lakes.  What  will  be  the  effect 
of  the  recently  completed  ship  canal  at  Chicago,  on  the  level  of  Lake 
Michigan  ? 

What  would  be  the  effect  on  the  character  of  the  water  were  the 
basin  of  the  Caspian  Sea  to  fill  until  it  overflowed  ? 

If  the  basin  of  the  Black  Sea  were  elevated  twenty  or  thirty  feet 
what  would  the  water  be,  salt  or  fresh  ? 


IMPERFECT  AND   OBSTRUCTED   DRAINAGE     185 

Mention  some  of  the  benefits  resulting  from  the  Great  Lakes  of  North 
America,  with  reference  to  commerce,  industries,  and  climate. 

Which  of  the  two  Great  Lakes  may  be  regarded  as  a  single  body  of 
water?     Why? 

The  level  reach  of  land  in  the  illustration,  p.  171,  was  formerly  a 
lake  ;  explain  how  it  became  the  flood  plain  of  a  mountain  stream. 

From  any  convenient  source  of  reference  write  a  description  of  Death 
Valley,  California,  or  of  the  Dead  Sea,  Syria. 

From  the  section  of  the  marsh  lakes,  p.  166,  prepare  a  description 
of  them,  concerning  their  depth,  altitude,  and  navigability. 

COLLATERAL   READING   AND    REFERENCE. 

Russell. — Lakes  of  Nevada,  Physiography  of  the  United  States, 
pp.  101-130. 
Le  Conte.— Elements  of  Geology,  pp.  80-82,  580-581. 
Shaler. — U.  S.  GeoL  Survey,  An.  Rep't,  1800. 

NOTES 

'  There  is  no  distinction  between  a  lake  and  a  pond,  except  the 
very  indefinite  one  of  size. 

'  Lakes  are  sometimes  formed,  however,  in  places  where  a  steep 
slope  joins  one  that  is  very  moderate.  Examples  of  such  lakes 
occur  in  the  eastern  slope  of  the  Scandinavian  Peninsula  and  in 
Nevada. 

=  Marsh  lakes  are  rarely  more  than  a  few  feet  in  depth.  They 
are  seldom  navigable,  and  conuuercially  they  are  of  but  little 
importance.  In  Europe  many  such  lakes  have  been  drained  in 
order  to  make  cultivable  land  of  their  beds.  There  are  several 
instances  where  such  basins  are  filled  with  water  and  used  for  fish 
culture  for  a  period  of  several  years,  and  then  drained  and  culti- 
vated for  a  like  period. 

*  Occasionally  lakes  are  formed  on  mountain-slopes  by  the 
agency  of  landslips,  but  they  are  seldom  long  Uveci.  Sometimes 
they  break  through  the  material  that  blocks  their  overflow,  but 
more  commonly  the  outflowing  water  cuts  a  channel  through  it 
deep  enough  to  drain  the  lake  to  the  bottom. 

'"Walled"  lakes  are  common  in  Iowa,  Minnesota,  and  Da- 
kota.     So  regular  are  the  walls  of  their  shores  that  for   many 


186  PHYSICAL   GEOGRAPHY 

years  it  was  fommonly  believed  they  were  artificial  and  were 
built  by  a  prehistoric  race  of  people.  As  a  matter  of  fact,  how- 
ever, the  walls  are  the  work  of  ice.  In  severe  winters  these  lakes 
freeze  nearly  to  the  bottom  ;  but  inasmuch  as  water  increases  in 
bulk  when  it  freezes,  tlie  ice,  in  expanding,  pushed  the  bowlders 
slioreward.  Time  and  time  again  this  process  was  repeated  until 
the  rocks  were  pushed  back  to  a  position  where  the  resistance  of 
the  earth  back  of  them  was  equal  to  the  pushing  force  of  the  ice. 

"  In  scraping  out  these  basins  not  the  ice  itself,  but  the  frag- 
ments of  rock  held  at  the  bottom,  form  the  cutting  tool. 

^  There  are  several  instances  in  which  flowing  lava  has  blocked 
up  a  river  channel  and  formed  a  lake.  In  at  least  two  places  the 
Columbia  River  was  thus  blocked,  and  the  high- water  marks  of 
the  lakes  formed  are  still  plainly  visible.  In  each  instance,  how- 
ever, the  river  succeeded  in  recovering  its  channel  and  the  lakes 
were  therefore  drained.  Accidental  lakes,  resulting  from  the 
blocking  of  a  river  channel  by  coulees  of  lava,  are  common  in 
volcanic  countries.  Still  another  accidental  lake  is  the  crater 
lake,  which  is  merely  an  old  volcanic  crater  filled  with  water. 
Crater  Lake,  in  Oregon,  and  Lucrine  Lake,  in  Italy,  are  exam- 
ples of  such  lakes.  The  former  is  about  2,300  feet  deep  and  is 
a  wonderfully  interesting  body  of  water. 

"  Not  only  have  coves  of  the  sea-shore  been  shut  off  by  bars, 
thus  forming  lagoons,  but  the  same  process  has  been  carried  on 
along  the  shores  of  lakes.  Such  lagoons  are  in  process  of 
formation  at  the  head  of  Lake  Superior,  Lake  Erie,  and  Lake 
Ontario.  In  each  case,  however,  the  formation  of  the  lagoon  is 
not  yet  complete,  owing  to  the  fact  that  the  current  from  the 
river  is  still  able  to  keep  a  channel  open. 

""  Albemarle  and  Pamlico  Sounds  are  examples,  and  they  re- 
main as  sounds  for  the  reason  given  in  the  preceding  note.  In 
other  words  the  sound  is  often  an  intermediate  stage  between  a 
bay  and  a  lagoon. 

'"  There  are  a  few  small  salt  lakes  having  outlets,  but  none  of 
importance.  They  are  saline  because  of  salt  springs  within  their 
basins.  Not  all  so-called  salt  lakes  contain  common  salt,  how- 
ever ;  in  many  various  alkaline  substances  are  found. 

"  Near  the  City  of  Mexico  formerly  there  were  several  lakes  that 
overflowed  into  a  fourth.  The  latter  is  salt,  the  others  not  drained 
are  fresh.     Utah  Lake  overflows  into  Great  Salt  Lake  through 


IMPERFECT  AND  OBSTRUCTED  DRAINAGE     187 

Jordan  River ;  its  waters  are  fresh.  Lake  Chad,  in  Africa,  is 
norinally  without  an  outlet.  Occasionally,  however,  in  seasons 
of  unusual  rains,  it  overflows  into  the  Libyan  Desert.  This 
occasional  ovei'flow  is  sufficient  to  keep  its  w'aters  fresh.  The 
waters  of  the  Caspian  Sea  are  kept  moderately  fresh  by  a  similar 
process.  On  its  eastern  border  is  a  gulf,  the  Karabogas,  con- 
nected with  the  main  body  of  the  lake  by  a  narrow  strait.  The 
watei'S  of  the  gulf  are  very  shallow,  and  so  great  is  tlie  evapora- 
tion, that  a  four  or  Ave  knot  current  is  constantly  flowing  into 
it  from  the  main  body.  From  this  inflow  about  250,000  tons  of 
salt  are  deposited  daily.  Now,  if  this  amount  of  salt  were  left 
dissolved  in  the  lake  the  latter  would  sooner  or  later  become  a 
saturated  brine.  But  because  of  this  separation  and  deposit  of 
salt,  the  waters  have  not  become  perceptibly  salter,  in  the  time 
since  measurements  have  been  made. 

'■  It  seems  a  contradiction  of  facts  to  assert  that  a  salt  lake 
may  become  fresh  by  a  process  of  drying  up  ;  nevertheless  this 
has  been  the  history  of  many  lakes.  During  a  long-continued 
period  of  deficient  rainfall,  a  lake  may  dry  up,  leaving  its  mineral 
salts  as  a  deposit  upon  the  bottom.  In  time  the  winds  cover 
tliis  saline  crust  with  a  thick  layer  of  fine  soil  ;  and  when  the 
lake  again  begins  to  All,  its  waters  are  fresh.  Pyramid  and  Win- 
nemucca  Lakes  in  Nevada  are  illustrations  ;  their  waters  are 
comparatively  fresh. 

'^  Lake  Agassiz,  a  body  of  Avater  considerably  larger  than  the 
five  great  lakes,  formerly  covered  a  large  part  of  the  valley  of  the 
Red  River  of  tlie  North.  The  destruction  of  this  body  of  water 
was  caused  probably  by  glacial  action.  It  had  several  outlets, 
one  of  which  Avas  the  present  channel  of  the  Minnesota  River. 

'*  This  lake  preceded  any  of  the  lakes  now  in  the  Basin  Region, 
and  was  older  even  than  the  Uinta  Mountains.  The  bed  of  the 
lake  seems  to  have  been  lowered,  and  this,  in  part,  was  probably 
one  factor  in  its  destruction. 

'^  It  is  not  unlikely  that  Lake  Moeris,  in  Egypt,  was  destroyed 
by  winds.  It  was  situated  a  few  miles  southwest  of  the  Nile 
delta  and  disappeared  within  historic  times  ;  but  until  within  a 
few  years  its  exact  position  was  not  known.  In  this  region  the 
movement  of  wind-blown  rock  waste  is  incessant,  and  the  amount 
moved  in  even  a  few  days  is  enormous.  Former  canals  across 
the  Isthmus  of  Suez,  one  after  another  have  been  filled  by  rock 


188  PHYSICAL   GEOGRAPHY 

waste,  and  there  is  every  appearance  to  suggest  that  the  isthmus 
itself  was  formed  largely  through  teolian  agency. 

'"  The  old  shore  lines  of  Great  Salt  Lake  are  still  a  marked 
feature,  and,  excepting  the  few  places  where  they  have  been 
obliterated,  they  have  been  surveyed  throughout  the  entire  cir- 
cuit of  the  lake.  Old  shore  lines  have  been  found  above  the 
present  level  of  Lakes  Titicaca  and  Maracaibo,  and  also  above 
the  level  of  the  lakes  of  the  western  part  of  the  Great  Basin. 
Two  old  shorelines  of  Lake  Ontario  have  been  found  in  New 
York,  one  of  which,  the  "Ridge  Road,"  may  be  traced  along 
nearly  the  whole  extent  of  the  southern  shore.  In  time  its 
level  has  been  somewhat  warped  and  it  has  now  a  grade  of  one  or 
two  feet  per  mile. 

"  In  many  instances  the  carbonates  of  alkaline  metals  are  pre- 
sent in  such  quantities  that  the  waters  of  the  lake  are  strongly 
alkaline.     Many  of  the  lakes  of  the  Great  Basin  are  alkaline. 

'"Lake  Maracaibo  is  a  lagoon  or  "clover-leaf"  bay,  rather 
than  a  lake  of  ordinary  character. 

'"  It  is  difficult  to  draw  the  line  between  marsh  lakes  and 
swamps  on  the  one  hand,  and  quite  as  difficult  to  distinguish 
between  the  latter  and  meadow  lands  on  the  other.  The  diflfer- 
ence  is  practically  one  of  degree.  A  lake  or  a  shallow  lagoon 
passes  through  all  the  intervening  stages. 

'°  In  many  instances  the  emergence  of  underground  waters  to 
the  surface,  by  percolation  (see  illustration,  p.  133),  causes 
swamps.  The  various  holsas  on  the  coast  plain  between  Los 
Angeles,  California,  and  the  ocean  are  formed  in  this  manner. 

'^  It  is  well  to  bear  in  mind  that  peat  is  not  a  plant,  but  a 
condition  of  imperfect  decojnjJosition  that,  under  certain  condi- 
tions, almost  all  vegetable  tissue  may  assume.  The  softer  and 
more  soluble  parts  of  the  tissue,  which  have  been  changed  to  a 
black  slime,  are  really  a  mixture  of  nearly  pure  carbon  and 
hydrocarbons  ;  the  wood  fibre  remains.  It  is  likely  that  the  in- 
correct popular  notion  has  arisen  from  the  fact  that  nearly  all 
the  peat  used  for  fuel  is  derived  from  species  named. 

^^  Although  all  lacustrine  swamps  are  old  lakes  that  have  been 
destroyed  by  vegetation,  not  all  of  them  become  peat- bogs.  In 
many  instances  the  lake  is  situated  north  or  south  of  the  lati- 
tude in  which  sphagnum  thrives.  The  peat-bogs  of  Ireland 
are  historic,  but  they  are  not  more  extensive  than  those  of  the 


IMPERFECT  AND  OBSTRUCTED  DRAINAGE  189 

Danube.  They  occur  in  nearly  every  country  in  which  sphag- 
num grows. 

^^  Quaking  bogs  are  very  common  in  the  swamps  of  the  South 
Atlantic  States.  Usually  the  mat  of  sphagnum  spreads  from  the 
margin  toward  the  centre,  but  in  many  instances  patches  of 
the  plant  accumulate  in  the  open  water,  forming  islands. 
Generally  the  insular  patches  are  attached  to  the  bottom,  but  not 
infrequently  they  float  hither  and  thither.  In  time  they  spread 
marginally  until  the  surface  is  finally  covered.  The  mat  of 
accumulated  sphagnum  receives  more  or  less  earthy  matter  and 
becomes  a  tolerably  firm  surface.  In  California  one  of  the  lines 
controlled  by  the  Southern  Pacific  Company  was  built  across  a 
quaking  bog  a  distance  of  several  miles.  It  finally  caved  in, 
however,  engulfing  several  cars  of  a  freight  train. 

^^  The  various  species  of  rush,  flag,  reed,  and  sweet  briar  are 
associated  Avith  swamps  and  contribute  not  a  little  to  their  for- 
mation. Tlie  wild  grape  and  several  species  of  wild  smilax  are 
also  abundant  in  swamps.  These  species,  liowever,  are  found 
mainly  south  of  the  latitude  in  wliich  sphagnum  thrives. 

^^  The  mud-Hat  stage  is  always  present;  it  is  merely  the  area  or 
belt  that  is  uncovered  at  low  tide.  If  the  slope  is  gentle  this 
belt  may  have  considerable  Avidth — and  this  is  the  case  along  the 
coast  of  the  South  Atlantic  States  and  the  shores  of  the  Gulf. 
Along  shores  swept  by  fairly  high  tides  the  mud-flat  belt  is 
usually  wide. 


CHAPTER  XI 

OCEAN   WATERS    AND    THEIR    MOVEMENTS:    WAVES, 
TIDES,    AND   CURRENTS 

Almost  all  the  plienomena  connected  Mitli  the  wasting^ 
of  the  laud,  with  climate,  and  even  with  the  existence  of 
life,  in  one  way  or  another  depend  on  the  sea.  In  at  least 
two  ways  the  sea  differs  from  other  bodies  of  water.  It 
is  many  thousand  times  the  size  of  the  largest  body  of 
fresh  water  and,  two  or  three  inland  lakes  excepted,  its 
surface  level  is  lower.  Practically  the  sea  supplies  the 
land  with  fresh  water,  and  because  of  its  lower  level,  al- 
most all  the  waters  of  the  land  sooner  or  later  flow  back 
into  it. 

Sea-water  is  briny  and  bitter ;  doubtless  it  has  always 
been  thus,  but  inasmuch  as  the  stream  waters  flowing  into 
it  are  constantly  dissolving  mineral  matter  from  the  rock 
waste  and  carrying  it  to  the  ocean,  the  amount  in  the  latter 
is  constantly  increasing.  Every  one  hundred  pounds  of 
sea-water,  on  an  average,  contains  about  three  and  one- 
half  pounds  of  saline  matter  ;  most  of  this  is  common  salt, 
the  remainder  being  chiefly  lime  and  magnesia.  The  per- 
centage of  mineral  matter  varies.  In  localities  where 
evaporation  is  rapid,  the  proportion  of  salt  is  larger. 
Thus,  in  the  Red  Sea'  it  is  more  than  four  per  cent., 
while  in  the  Baltic  Sea  it  is  less  than  one-half  as  great. 
It  is  somewhat  greater  in  tropical  than  in  polar  regions. 

Bulk  for  bulk,  sea-water  is  heavier  than  fresh  water.  A 
cubic  foot  of  fresh  water  weighs  about  1,000  ounces ;  on 

190 


192  PHYSICAL   GEOGRAPHY 

account  of  its  miiieml  matter  the  same  volume  of  sea- 
water  weighs  at  least  thirty-five  ounces  more.  Tempera- 
ture also  affects  the  density  of  water  ;  if  1,000  cubic  inches 
of  water  at  the  freezing-point  be  heated  to  the  temperature 
of  a  hot  summer  day,  its  volume  will  be  increased  seven  or 
eight  cubic  inches.  The  differences  in  temperature  and 
density  have  far-reaching  results ;  for  upon  these  varia- 
tions the  general  circulation  of  the  waters  of  the  sea  in 
part  are  due. 

The  temjjerature  of  the  sea  varies  with  both  latitude  and 
depth.  In  general,  the  surface  waters  of  equatorial  I'e- 
gions  are  warmest,  and  in  the  broader  extents  of  the  sea 
their  temperature  is  not  far  from  26°  (79°  F.).  Toward  the 
poles  it  gradually  falls,  and  in  polar  regions  it  is  rarely 
much  above  the  freezing-point.  The  variation  of  temper- 
ature with  latitude  is  by  no  means  uniform,  however,  for 
in  various  places  warm  water  dragged  by  the  "  skin  fric- 
tion" of  winds  is  frequently  found  in  high  latitudes. 

With  relation  to  depth  the  variation  is  remarkably  uni- 
form. In  low  latitudes  the  bottom  temperature  of  deep 
water  is  a  degree  or  two  above  the  freezing-point  of  fresh 
water ;  in  polar  latitudes,  a  degree  or  two  below  it.  In 
shallow  waters  and  land-locked  basins,  however,  the  varia- 
tions in  temperature  are  usually  very  irregular.  Thus,  the 
entrance  to  the  Gulf  of  Mexico  is  blocked  by  a  submarine 
ridge  whose  crest  is  1,200  feet  below  the  surface,  and  be- 
cause of  this,  water  whose  temperature  is  lower  than  that  of 
the  1,200-foot  level  cannot  enter  the  Gulf.  But  even  at  a 
depth  of  12,000  feet,  the  temperature  varies  but  little  from 
that  of  the  1,200-foot  level 

The  freezing  temperature  of  salt  water  is  lower  by  two  or 
three  degrees  than  that  of  fresh  water,  the  difference  de- 
pending mainly  on  the  amount  of  mineral  salts  in  solu- 
tion.    The  ice  of  the  sea  is  therefore  formed  in  high  lati- 


WAVES,    TIDES,    AND    CURRENTS 


193 


tudes,  where  the  temperature  is  much  belmv  the  freezing- 
point."^ 

Sea-ice  takes  various  forms.^  The  nearly  level  and  nar- 
row shelf  that  in  polar  regions  forms'  along  the  shore,  and 
skirts  almost  its  entire  extent,  is  called  the  ice-foot.  Any 
considerable  extent  of  undisturbed  or  unbroken  ice  forms 
an  ice-sheet  or  ice-field.  When  on-shore  winds  become  so 
strong  that  the  ice-field  is  crushed  and  piled  up  against  the 


ICH   OF   THE    SEA  ;    FLOE,    PACK,    AND    BERG. 


shore,  it  forms  pack  ice.*  Detached  masses  floating  about 
constitute  y?oes;  finely  broken  ice  floating  on  the  surface 
constitutes  sludge. 

A  small  part  of  the  ice  is  caught  by  currents  and  winds, 
and  earned  into  warmer  latitudes,  where  it  finally  melts. 
By  far  the  greater  part,  however,  never  leaves  polar  re- 
gions ;  possibly  in  a  few  instances  it  accumulates,  but 
most  of  it  melts  during  the  l)ri(f  polar  summer.  A  certain 
amount  of  ice  certainly  floats  into  temperate  latitudes,  in 


194 


PHYSICAL   GEOGEAPHY 


the  form  of  icebergs,  but  this  ice  is  not  born  of  the  sea ;  it 
is  fresh  water  ice  that  is  formed  on  land,  and,  in  the  form 
of  glaciers,  moves  down  the  slopes  until  it  breaks  off." 

Waves. — The  alternate  rising  and  falling  of  successive 
ridges  of  water  form  waves.     Thej  vary  in  size  from  the 


STORM   WAVES  :    SURF    BREAKERS. 

tiny  ripples  made  by  a  summer  breeze,  to  the  huge  billows 
that  toss  the  largest  ships.*^  Every  body  of  water  upon  the 
earth  is  swept  by  waves,  and  these  are  caused  by  the  fric- 
tion of  the  air  against  the  surface  of  the  water.^ 

The  motion  of  the  water  of  the  wave  is  simply  up  and 
down,  with  a  possible  rotatory  movement ;  and  if  the  wind 
ceases  for  a  moment,  the  i^heory  holds  true.      Under  a 


WAVES,    TIDES,    AND    CURRENTS  195 

strong  wind,  however,  the  top  of  the  wave  is  pushed  for- 
ward, and  if  the  gale  be  very  strong  it  breaks  into  foam, 
forming  "white  caps"  and  "scud."  Before  the  strongest 
storm-winds  not  a  little  water  is  blown  into  spray,  and  the 
whole  surface  of  the  ocean  is  covered  with  foam. 

"When  waves  roll  in  upon  a  shallow  coast  their  motion 
is  also  modified.  The  moment  the  bottom  of  the  wave 
touches  gi'ound  it  begins  to  drag.  The  top  of  the  wave, 
on  the  contrary,  not  beiug  impeded,  advances  more  rapidly, 
and  finally  comb.s  or  falls  forward,  making  breakers.  The 
water  and  foam  that  flow  upon  the  shore  constitute  the 
surf. 

The  distance  from  the  shore  at  which  waves  begin  to 
comb  depends  partly  on  the  depth  of  the  wave,  and  partly 
on  the  depth  of  water  along  the  shore.  Ordinary  waves 
rarely  exceed  three  or  four  fathoms  in  dej^th,  and  therefore 
do  not  comb  until  they  are  within  a  few  rods  of  the  shore. 
Along  certain  shores  of  the  Indian  Ocean,  on  the  other 
hand,  where  the  coast  waters  are  shallow  and  the  waves 
are  deep,  the  latter  begin  to  comb  at  a  distance  of  three 
or  four  miles  from  shore. 

For  the  formation  of  the  highest  and  largest  waves,  a 
deep,  open  sea  is  required,  and  in  general  the  largest  waves 
are  found  in  the  broadest  expanse  of  water.  In  calm 
weather,  the  waves  of  the  open  sea  are  from  six  to  ten 
feet  in  height ;  their  breadth  is  about  ten  times  the  height. 

With  a  wind  of  twenty  or  thirty  miles  an  hour,  the 
height  of  the  wave  is  somewliat  increased;  its  breadth  is 
materially  greater,  and  the  largest  steamships  pitch  con- 
siderably as  they  ride  over  thoui.  With  the  wind  at  sixty 
or  eighty  miles  the  breadth  of  tlie  wave  is  increased  to 
about  two  thousand  feet ;  its  height  may  reach  twenty  or 
thirty  feet,  and  its  progressive  velocity  may  reach  forty 
miles  an  hour. 


I'jG  riiisiuAL  (;eography 

It  is  a  couimoii  belief  that  the  waves  run  highest  when 
the  wind  is  at  its  maximum  velocity.  This  is  not  the  case, 
however ;  they  do  uot  reach  their  greatest  height  until  the 
lull  of  the  wind  ;**  then  they  sometimes  roll  to  a  height  of 
fortj'-five  or  fifty  feet. 

The  force  with  which  waves  strike  an  opposing  surface 
is  greater  than  is  generally  imagined.  Measurements  on 
the  coast  of  Scotland,  show  that  ordinary  calm-weather 
waves  have  a  striking  force  of  six  hundred  pounds  per 
S(|uare  foot ;  that  of  the  heaviest  storm-waves  is  about  ten 
times  as  great. 

In  navigation  it  is  found  that  the  chief  damage  from 
storm-waves  is  due  to  the  battering  that  the  lighter  wood- 
work above  deck  receives.^  In  recent  years  the  old  cus- 
tom of  spreading  oil  on  the  surface  to  the  windward  has 
been  revived.'"  The  oil  covering  the  water  presents  a 
surface  that  offers  comparatively  little  friction  to  the  wind. 
As  a  result  the  waves,  although  rolling  high,  no    longer 


THE    TIDE   WAVE;    MOON    IN    CONJUNCTION 

break  upon  the  vessel.  The  latter,  therefore,  is  often 
enabled  to  withstand  storm-waves  that  otherwise  would 
demolish  everything  above  her  decks. 

Notwithstanding  their  tremendous  energy,  waves  are 
superficial.  The  effects  of  ordinary,  calm-weather  waves 
do  not  extend  more  than  a  few  feet  below  the  surface  ; 
the  fiercest  storm-waves  do  not  reach  more  than  two  hun- 
dred feet  below  the  surface. 


WAVES,    TIDES,    AND   CURRENTS  197 

Tides. — The  alternate  rise  aud  fall  of  the  sea-level  ^ 
twice  a  claj  is  a  pheuomenon  familiar  to  everyone  who 
has  visited  the  seashore.  For  six  hours  the  level  of  the 
water,  little  by  little  rises,  overflowing  the  shore  and  fill- 
ing the  river  estuaries.  For  a  few  moments,  the  water  is 
stationary,  and  then  for  about  six  hours  it  falls — ever 
repeating,  never  ceasing  its  oscillations. 

Excepting  certain  estuaries  and  bays,  neither  the  high 
nor  the  low  water  level  varies  much  throughout  the  year. 
As  the  level  rises  and  the  water  flows  in  upon  the  shore. 


THE   TIDE   WAVE  :    MOON    IN   OPPOSITION 

the  tide  mjfnrx/ ;  as  it  recedes  it  is  ehl) ;  its  highest  level  is 
Iiiyh  vxifer,  and  its  lowest  loio  wafer.  During  the  few 
minutes  at  the  turn  of  the  tide  it  is  slack  wafer. 

This  rise  and  fall  of  water  is  ascribed  to  the  attraction 
of  the  sun  and  the  moon ;  in  its  nature,  the  movement  of 
the  water  is  practically  a  wave  several  thousand  miles 
broad.  Both  the  sun  and  the  moon  attract  the  earth. 
The  solid  portion  of  the  earth  being  rigid,  however,  does 
not  perceptibly  bend  or  yield ;  the  water  envelope,  on 
the  contrary,  is  drawn  into  the  elongated  form,"  giving 
the  appearance  of  two  wave-crests,  one  on  each  side  of  the 
earth.  No  matter  whether  the  sun  and  the  moon  are 
on  the  same  side,  or  on  opposite  sides,  their  combined 
attraction  will  produce  the  same  results.  If,  however, 
they  have  the  position,  so  that  they  pull  at  right  angles, 
four  tide- waves  will  be  formed — two  of  the  sun  and  two 
of  the  moon. 


198  PHYSICAL   GEOGRAPHY 

In  most  of  the  Northern  Hemisphere,  where  the  great 
land  masses  interrupt  the  progress  of  the  tide- waves,  the 
solar  tides  are  merged  into  those  of  the  moon.  Only  in 
the  broad  expanse  of  the  ocean,  in  the  islands  of  the 
South  Pacific,   are    they   distinguishable.      When    their 

effects  are  added  to  or 
subtracted  from  the  lu- 
nar waves,  however,  the 
difference  is  consider- 
able. Thus,  at  new  and 
full  moon,  when  the  pull 
is  exerted  in  a  straight 

THE  TIDE:    MOON   IN   QUADRATURE  ^^^^  ^^^^  ^ideS  are  SOmC- 

what  higher  at  flood 
and  lower  at  ebb  ;  these  are  the  spring  tides.  When  the 
attraction  is  exerted  at  right  angles  they  are  necqy  tides. 
In  some  instances  the  spring  tides  are  twice  as  high  as 
the  neap  tides. 

Thus  it  seems  that  the  moon  by  its  attractive  force  lifts 
the  waters  of  the  sea  into  two  great  waves.  Moreover,  as 
the  moon  revolves  around  the  earth,  these  waves  are  each 
dragged  around  at  the  same  time,  in  much  the  same 
manner  as  though  they  were  fastened  to  it,  each  making  a 
passage  in  about  twenty-eight  days. 

But  while  these  waves  are  making  each  its  revolution, 
the  earth  at  the  same  time  is  turning  on  its  axis,  every 
twenty-four  hours.  The  daily  motion  of  the  tides,  there- 
fore, results  from  the  earth's  turning  on  its  axis.  Every 
point  on  the  earth,  accordingly,  overtakes  and  passes  the 
two  waves  daily,  very  much  as  though  it  were  slipping 
under  them. 

If  the  surface  of  the  earth  were  covered  with  a  uniform 
depth  of  water,  the  direction  of  the  tide-waves  would  be 
from  east  to  west.     As  a  matter  of  fact,  the  position  of  the 


WAVES,    TIDES,    AND    CURRENTS 


199 


continents  prevents  an}'  sucli  uniform  direction.  Every 
mass  of  land  is  an  obstacle  in  the  path  of  the  advancing 
wave,  and  inasmuch  as  the  Litter  cannot  sweep  over  a  con- 
tinent, it  must  pass  around  it,  or  be  checked. 

Only  in  the  broad,  open  waters  of  the  Southern  Hemi- 
sphere do  the  tides  move  in  their  theoretical  direction  from 
east  to  west.     In  the  North  Atlantic  the  wave  is  turned 


CO-TIDAL   LINES 
Tile  Una  show  Ihc  position  of  the  crest  of  the  tide-wave  for  each  two  hours. 


to  the  northward,  and,  entering    the    Arctic  Ocean,  it  is 
diverted  to  the  eastward.^ 

The  height  of  the  tides  is  also  affected  by  the  land 
masses.  In  mid-ocean  the  difference  between  high  water 
and  low  water  is  scarcely  three  feet.  Along  the  coast  of 
the  United  States  it  varies  from  four  to  ten  or  twelve  feet. 
From  New  York  to  Savannah  spring  tides  are  about  five 
feet,  and  neap  tides  about  four  feet.  In  the  Gulf  of 
Mexico  the  rise  and  fall  is  only  about  one-half  as  great ; 


200  PHYSICAL   GEOGRAPHY 

along  tlie  Maine  coast  it  is  ten  or  twelve  feet;  and  at 
Sitka,  Alaska,  from  twenty  to  thirty  feet. 

The  great  difference  is  due  chiefly  to  the  shape  of  the 
shores.  If  the  tide-wave  faces  a  V-shaped  estuary  the 
advancing  body  becomes  constricted  by  the  narrowing 
shores.  Not  being  able  to  spread  out  sideways,  it  is 
therefore  increased  both  in  depth  and  velocity.  In  Minas 
Basin,  at  the  head  of  the  Bay  of  Fundy,  at  times  the  water 
advances  as  a  solid  wall  twenty  or  thirty  feet  high.  The 
piling  up  of  tide-waters  in  the  form  of  a  wave  is  commonly 
called  a  bore.  It  is  a  marked  feature  in  the  Amazon,  the 
Ganges,  and  the  rivers  of  the  China  coast.  It  is  also 
noticeable  in  many  of  the  estuaries  of  the  British  Isles. 
The  spring  tide  in  Bristol  Channel  is  sometimes  forty  feet. 

In  many  instances  the  shape  of  the  shore  is  such  that 
the  waters  of  the  advancing  tide  are  separated  by  an 
island  lying  near  the  shore,  again  uniting  in  the  narrow 
strait  between  the  mainland  and  the  island.  As  a  result 
eddies  and  dangerous  whirls  are  formed.  Thus,  at  Long 
Island  the  advancing  wave  is  divided,  one  part  entering 
New  York  Bay,  the  other,  Long  Island  Sound.  The  two 
currents  meet  in  the  narrow  Hell  Gate,  or  "whirling  strait." 
The  Maelstrom,  an  eddy  formed  by  the  Lofoten  Islands, 
off  the  coast  of  Norway,  is  a  similar  current.^^ 

Ocean  Currents. — Throughout  the  greater  part  of  its 
extent  the  sea  is  traversed  by  currents  that  flow  in  defi- 
nite directions  with  a  fairly  uniform  velocity.  The  water 
of  an  ocean  current  has  an  energy  of  its  own,  and  its  mo- 
tion is  practically  the  same  as  though  it  were  flowing  from 
a  higher  to  a  lower  level.  There  are  other  instances,  how- 
ever, in  which  the  movement  is  almost  entirely  caused  by 
the  wind,  the  direction  being  wholly  a  result  of  the  wind. 
The  wind-blown  Avaters  are  called  drifts.  Currents  are 
deep,  sometimes  extending  to  the  bottom  ;  drifts,  on  the 


202  PHYSICAL  GEOGKAPHY 

other  hand,  are  superticial.  The  current  may  gradually 
become  a  drift,  and  a  drift  may  become  a  current. 

The  winds,  and  the  unequal  heating  of  the  Avaters  in 
equatorial  and  polar  regions  are  thought  to  be  the  main 
causes  of  the  general  movement  of  ocean  waters ;  the 
winds  and  the  rotation  of  the  earth  on  its  axis  are  the 
chief  factors  that  make  them  currents  and  determine 
the  direction  of  their  liow.'^  The  water  in  equatorial  re- 
gions receiving  the  vertical  rays  of  the  sun  is  heated  to 
a  higher  temperature  than  the  water  in  higher  latitudes. 
Being  expanded  a  flow  toward  polar  regions  occurs.  At 
the  same  time  cooler  water  flows  toward  the  equator  in  the 
form  of  an  undercurrent.  Thus  a  constant  circulation  is 
taking  place — a  surface  movement  from  equatorial  to  po- 
lar and  an  undercurrent  from  polar  to  equatorial  latitudes. 
This  general  movement  is  modified  by  the  winds — and 
undoubtedly  by  the  rotation  of  the  earth. ^^ 

In  equatorial  latitudes  the  prevailing  direction  of  the 
wind  is  toward  the  west,  and  this  gives  the  waters  a  west- 
erly movement.  A  flow  of  water,  nearly  1,000  miles  broad, 
called  the  Equatorial  Current,  is  the  result,  and,  except  at 
the  places  where  it  is  interrupted  by  the  continents,  it 
girdles  the  earth.  Its  flow  is  scarcely  more  than  a  drift, 
and  its  rate  is  about  ten  or  fifteen  miles  per  day.  Most 
of  the  warm  currents  of  high  and  temperate  latitudes  are 
branches  of  it. 

The  Atlantic  part  of  this  current  is  divided  at  the  east- 
ern angle  of  South  America.  The  southern  branch  flows 
along  the  eastern  coast  of  this  grand  division  for  nearly 
2,000  miles;  what  is  its  name?  Gradually  losing  its 
energy  it  becomes  a  drift,  and  finally  it  returns  to  the 
equatorial  current.  Describe  the  course  of  the  northern 
branch ;  what  is  its  name  after  it  emerges  from  the  Carib- 
bean Sea  ?     The  Pacific  part  of  the  Equatorial  Current  is 


WAVES,    TIDES,    AND    CURREXTS  203 

more  than  9,000  miles  long.  At  the  edge  of  the  Eastern 
Continent  it  is  again  divided;  what  is  the  name  of  the 
northern  branch  ?  of  the  southern  ?  Describe  the  circuit 
of  each.  In  the  midstream  of  the  Equatorial  Current  is 
found  a  narrow  belt  of  water  flowing  in  the  direction  op- 
posite that  of  the  main  stream.  It  is  called  the  Equa- 
torial Counter  Current ;  no  satisfactory  explanation  for  it 
is  known. 

The  Gulf  Stream  is  by  far  the  most  important  of  the 
cm-rents  of  the  Atlantic  Ocean  ;  Avhy  ?  Its  sources  are  in 
the  Caribbean  Sea.  A  part  of  its  volume  flows  through 
Santarem  Channel ;  a  greater  part  is  gathered  into  Yuca- 
tan Channel ;  a  small  but  measurable  part  is  drawn  from 
the  Gulf  of  Mexico.  These  branches  unite  in  Florida 
Strait,  and  here  the  stream  as  a  definite  current  begins. 

At  Florida  Strait  its  velocity  varies  from  three  and  one- 
half  to  five  and  one-half  miles  an  hour.^^  To  the  north- 
ward it  graduall}^  decreases  until,  oft'  the  Labrador  coast, 
it  ceases  to  have  any  motion  of  its  own ;  thereafter  it  is  a 
drift  dragged  by  westerly  Avinds. 

The  Gulf  Stream  is  not  only  the  swiftest  of  ocean  cur- 
rents, but  it  is  also  the  warmest.  Off  the  Florida  coast 
its  summer  temperature  is  30°  (86°  F.),  and  even  near  the 
Greenland  coast  it  is  twenty  or  thirty  degrees  (F.)  warmer 
than  the  surrounding  waters.  Contrary  to  common  opinion, 
it  is  not  a  shallow  current.  As  a  matter  of  fact,  from  Flor- 
ida Strait  to  Cape  Hatteras,  it  extends  to  the  bottom  of 
the  ocean.  Its  drift  is  pushed  northward  and  eastward, 
and  much  of  it  forms  a  circuit  returning  to  the  Equatorial 
Current.  A  considerable  vohime,  keeping  northward,  finds 
an  entrance  to  the  gulfs  and  bays  of  western  Europe,  reach- 
ing even  to  the  north  coast  of  Norway. 

The  Knrn  Siiro  is  the  Gulf  Str(>ain  of  the  Pacific. 
Some  of  its  waters  issue  from  the  Bay  of  Bengal,  but  the 


204  PHYSICAL   GEOGRAPHY 

greater  part  of  its  volume  passes  among  the  Malaysian 
Islands.  Thence  it  flows  along  the  eastern  coast  of  Asia. 
Off  the  Japan  Islands  it  becomes  a  drift,  and  its  waters 
are  then  pushed  by  the  prevailing  winds  toward  the  North 
American  coast,  performing  an  oval-shaped  circuit  like 
that  of  the  Gulf  Stream. 

The  Kuro  Siwo  is  not  only  a  much  feebler  current  than 
the  Gulf  Stream,  but  it  is  a  cooler  stream  as  well.  Its 
summer  temperature  rarely  exceeds  22°  (72°  F.),  and  its 
Avinter  temperature  is  not  far  from  17°  (63°  F.).  In  sum- 
mer it  extends  as  far  north  as  the  Kuril  Islands ;  in  win- 
ter it  scarcely  reaches  the  Japan  coast.  Recent  surveys 
show  that,  contrary  to  common  opinion,  no  part  of  the 
Kuro  Siwo  enters  the  Arctic  Ocean  through  Bering  Strait. 
In  a  few  instances  only  has  a  setting  of  water  into  the 
strait  been  observed,  and  these  have  resulted  from  strong 
southwesterly  winds.  The  prevailing  movement  in  Bering 
Strait  is  a  feeble  flow  from  the  Arctic  Ocean. 

It  has  been  definitely  ascertained  that  much  of  the  cir- 
culation of  the  colder  waters  of  the  ocean  takes  the  form 
of  undercurrents,  but  no  survey  of  an  undercurrent  has  yet 
been  made.  Two  very  definite  surface  currents  of  water 
have  been  observed,  however,  and  their  j^osition  is  fairly 
well  known.  These  are  the  Arctic  Currents.  One  of  them 
flows  southwards  along  the  east  shore  of  Greenland,  finally 
turning  into  Baftin  Bay  ;  the  other  flows  on  the  west  shore 
and,  emerging  into  the  Atlantic,  meets  the  Gulf  Stream  off 
Newfoundland. 

Oft'  the  coast  of  Cape  Hatteras,  almost  in  the  track  of 
the  Gulf  Stream,  is  an  adverse  current  known  on  pilot 
charts  as  "  Little  Hell."  It  is  marked  by  heavy,  choppy 
waves,  and  persists,  even  in  the  face  of  a  strong  southerly 
wind.  Its  waters  are  cold,  and  it  is  thought  to  result  from 
the  rising  of  an  arctic  undercurrent  to  the  surface. 


WAVES,   TIDES,   AND   CURRENTS  205 

The  Antarctic  Current  is  the  chief  movement  of  cold 
water  in  the  southern  hemisphere.  It  is  a  drift  rather 
than  a  definite  current,  however.  Its  waters  are  several 
degrees  cooler  than  those  with  which  they  finally  com- 
mingle. 

Economy  of  Ocean  Currents. — One  of  the  chief  and 
most  important  effects  of  marine  currents  is  the  equalizing 
of  the  temperature  of  ocean  waters.  Without  this  inter- 
change the  heat  of  equatorial  Avaters  would  sooner  or  later 
become  fatal  to  many  forms  of  life,  and  the  polar  ice-caps 
would  intrude  far  into  temperate  latitudes.  The  more 
practical  effects  are  seen  by  comparing  the  coast  of  Labra- 
dor with  that  of  the  British  Isles,  in  the  same  latitude. 
The  harbors  of  the  former  are  blocked  with  ice  for  five  or 
six  months  of  the  year  ;  the  latter  is  open  the  year  round. 
The  former  is  bathed  by  cold  waters ;  the  latter  by  the 
drift  of  the  Gulf  Stream.  The  port  of  Hammerfest,  situ- 
ated within  the  Arctic  circle,  is  an  open  harbor  free  from 
obstractive  ice  all  the  year  round.  It  is  very  doubtful  if 
warm  currents  have  any  perceptible  effect  on  the  tempera 
tui'e  of  a  region  at  any  considerable  clistance  from  the 
coast,  but  that  they  keep  the  coast  free  from  ice  is  beyond 
question.     How  does  this  affect  commerce? 

Evaporation  is  very  great  along  the  courses  of  warm  cur- 
rents and  the  moisture  borne  with  the  wind  adds  no  little 
to  the  rainfall  of  the;  regions.  When  the  moisture  is  con- 
densed the  latent  heat  set  free  adds  warmth  to  the  region. 
Cold  currents  hav(^  a  chilling  effect  on  the  air,  and  if  the 
latter  has  nincli  moisture  it  is  apt  to  take  the  form  of  fog. 
The  Newfoundland  and  Labrador  coasts  probably  get  their 
dense  fogs  in  this  way.  Ocean  currents  thus  are  indi- 
rectly factors  in  c-lin)ate. 

Sargasso  Seas. — Within  the  ovals  formed  by  the 
branches  of  the  J^jquatorial  Current  and  their  drifts  there 


206  PHYSICAL   GEOGRAPHY 

are  extensive  accumulations  of  marine  plants.  These  were 
named  by  Spanish  navigators  Zargazzo,  or  grassy  seas. 
The  accumulations  have  been  sometimes  attributed  to  the 
eddying  motion  of  the  current  and  its  drift,  but  of  this 
there  is  little  or  no  evidence.  Calm  water  is  necessary  for 
the  growth  of  these  species  forming  the  accumulations,  and 
they  occur  most  frequentl}^  in  such  localities. 

Physiographic  Effects  of  Oceanic  Movements. — 
So  closely  related  to  one  another  is  the  work  of  waves, 
tides,  and  currents,  that  their  physiographic  effects  can- 
not well  be  separated  one  from  the  other.  In  general  the 
work  of  waves  is  both  destructive  and  constructive — they 
not  only  tear  away  coasts,  but  they  build  them  as  well. 
On  the  other  hand,  the  work  of  tides  and  currents  is 
mainly  transporting — they  carry  material  from  one  place 
to  another.  Although  waves  act  only  at  the  surface,  their 
Avork  is  none  the  less  effective,  and  throughout  the  whole 
extent  of  coast  one  or  the  other  of  two  things  is  con- 
stantly going  on — material  is  either  being  removed  from 
the  shore  or  else  it  is  being  added  to  it. 

The  rugged  outlines  of  coasts  to  a  considerable  extent 
are  results  of  wave  action.  The  softer  parts  are  Avorn  and 
broken,  while  the  harder  portions  that  remain  largely  con- 
tribute to  the  frayed  appearance  of  the  coast.^'  At  first 
the  harder  rock  projects  in  the  form  of  long  arms ;  then 
these  are  broken,  leaving  a  multitude  of  rocky  islets. 

Along  the  coast  of  the  South  Atlantic  States,  the  effects 
in  places  are  still  more  noticeable.  The  shores  of  Cape 
May,  New  Jersey,  are  wasting  away  at  the  rate  of  several 
feet  a  year,  and  those  of  Charleston  Harbor  require  almost 
constant  repair,  so  destructive  is  the  incessant  pounding 
of  the  waves. 

On  the  east  coast  of  England,  owing  both  to  waves 
and  swift  tidal  currents,  the  yearly  Avaste  is  considerable, 


WAVES,    TIDES,    AXD    CURREN^TS  207 

and  since  the  time  of  Henry  YIII.  a  belt  about  one  mile 
in  width  has  been  shorn  from  the  Kent  coast.^^  Along 
the  west  coast  of  Scotland,  and  especially  among  the 
Hebrides  Islands,  are  many  thousand  rocky  islets  rising 
from  the  sea  like  spectral  watch-towers.  They  are  all  that 
remain  of  a  former  coast  as  witnesses  of  the  destructiye 
force  of  the  wayes. 

As  its  name  indicates,  a  cliff-girt  coast  is  one  that  is 
bordered  by  steep  or  by  vertical  cliffs.  The  chalk  cliffs 
of  Dover,  England ;  the  cliffs  at  Newj)ort,  Rhode  Island  ; 
and  almost  the  whole  extent  of  the  California  coast  are 
examples  of  this  t^^pe.  Generally  there  is  a  narrow  strip 
of  sandy  beach  between  the  cliff  and  the  water's  edge,  but 
sometimes  this  is  absent.  In  every  case  the  cliffs  are 
shaped  by  the  action  of  waves.  On  account  of  a  slow  sub- 
sidence of  the  coast,  the  sea  has  encroached  on  the  land, 
and  little  by  little,  the  waves  have  undermined  and  bat- 
tered down  the  shores. 

The  constructive  and  building  power  of  waves  is  finely 
shown  along  the  coast  of  the  South  Atlantic  and  Gulf 
States  and  that  of  the  Netherlands,  the  most  noticeable 
feature  of  which  is  the  multitude  of  spits,  barrier  beaches, 
and  islands  that  border  it. 

In  the  l)uilding  of  shores  not  a  little  depends  on  the 
position  and  direction  of  tides  and  local  currents.  If  the 
latter  strike  the  shore  broadside,  or  at  right  angles,  the 
Ijars  and  spits  take  the  shape  so  comrtion  along  the  Gulf 
coast.  On  the  other  hand,  if  they  impinge  upon  the 
shore  obliquely,  the  sand  and  sediment  are  caught  by  the 
swirl  of  the  current,  and  dej)osited  in  curved  forms  vari- 
ously known  as  sandy  hools. 

Forms  of  this  character  are  the  rule  along  the  Massa- 
chusetts coast.  Ca])e  Cod,  Mononioy  Point,  and  Nan- 
tucket Beach  are  nothing  but  sandy  hooks ;  Marthas  Vine- 


208  PHYSICAL   GEOGRAPHY 

yard  and  Nantucket  Islands  contain  half  a  score  of  such 
examples.  Sandy  Hook  Peninsula,  now  an  island  and  an 
obstruction  to  the  navigation  of  Lower  New  York  Bay,  is 
one  of  the  most  striking  examples.  Find  similar  examples 
on  the  shores  of  the  Nortli  and  Baltic  Seas. 

The  effects  of  the  tide  in  scouring  out  estuaries  have 
already  been  noted,  but  there  are  certain  effects  of  tidal 
currents  that,  at  first,  are  not  obvious.  Waves  are  capa- 
ble of  battering  down  a  cliff,  but  they  are  not  able  to  re- 
move the  material,  and  this,  in  time,  lodging  at  the  foot  of 
the  cliff,  would  protect  it  from  any  further  assaults  of  the 
waves.  But  if  the  tidal  currents  remove  this  material,  the 
waves  have  an  unprotected  surface  upon  which  to  work. 

The  bars  at  the  mouths  of  rivers  are  nearly  always  the 
work  of  tidal  currents,  and  so  are  many  of  the  "  banks  "  or 
shoals  that  obstruct  straits  and  sounds.  The  North  Sea 
contains  many  examples,  and  Lower  New  York  Bay  is  so 
full  of  them  that  only  a  small  part  is  available  for  deep- 
draught  vessels. 

Ocean  currents  undoubtedly  transport  an  enormous 
amount  of  material.  The  Gulf  Stream  sweeps  the  shells  of 
certain  marine  organisms  from  the  Caribbean  Sea  as  far 
north  as  the  Carolina  coast.  The  icebergs  floated  by 
arctic  currents  bring  down  a  large  amount  of  gravel  and 
bowlders  which  are  finally  dropped  in  lower  latitudes. 
Both  the  bank  on  which  the  Florida  Reefs  are  built,  and 
that  on  which  the  Bahamas  have  been  formed,  are  thought 
to  have  been  the  work  of  marine  currents.  It  is  by  no 
means  impossible  that  constant  deposition  of  matter  car- 
r'od  by  ocean  currents  may  have  resulted  in  extensive 
changes  of  level  in  various  parts  of  the  earth's  surface. 


QUESTIONS  AND  EXERCISES.— If    possible,  evaporate   a  small 
quantity  of  stream  water  of  any  kind  in  a  beaker,  or  a  porcelain  dish, 


WAVES,   TIDES,    AND   CURRENTS  209 

and  note  the  result.  Repeat  the  experiment  with  rain  water.  What 
inferences  can  be  drawn  that  are  applicable  to  the  second  paragraph  of 
this  chapter  ? 

Prove  that  ice,  bulk  for  bulk,  is  lighter  than  water. 

If  possible  observe  the  effects  of  waves  on  the  shore  of  any  conven- 
ient body  of  water.  Note  the  character  of  the  work  they  do,  or  that 
you  find  they  have  done.     Explain  how  waves  make  beach  sand. 

If  you  are  near  the  ocean,  find  the  season  of  the  year  when  the  tides 
are  highest. 

Refer  to  the  map,  p.  199,  and  note  the  direction  of  the  tide  waves  in 
various  parts  of  the  Atlantic  Ocean.  What  is  their  general  direction  in 
the  South  Pacific  ? 

Explain  how  ocean  currents  may  affect  navigation,  either  favorably 
or  adversely. 

In  one  of  the  first  chapters  of  his  narrative,  Robinson  Crusoe  speaks 
of  the  great  indraught  of  the  Gulf  of  Mexico ;  what  feature  is  meant  ? 

Of  several  thousand  sealed  and  registered  bottles  thrown  into  the 
Gulf  Stream,  off  the  Florida  Coast,  a  number  were  found  afterward  in 
the  Caribbean  Sea,  along  the  West  Indies  ;  from  the  current  chart,  p. 
201,  explain  their  movement. 

From  any  available  cyclopedia,  or  other  work  of  reference,  prepare 
an  account  of  one  or  more  of  the  following  :  the  Gulf  Stream,  the  Mael- 
strom, the  bore  of  the  Amazon,  the  tides  of  the  Bay  of  Fundy,  the 
Hell  Gate,  or  the  effects  of  storm-waves. 

COLLATERAL   READING   AND   REFERENCE. 

PiLLSBUKY.— The  Gulf  stream.     United  States  Coast  Survey. 

Mill. — Realm  of  Nature,  pp.  154-184. 

Shaler.— Sea  ami  Laml,  pp.  1-74,  187-222. 

U.  S.  Hydrographic  Office. — Use  of  Oil  in  Storms. 


NOTES 

'  Color  names  are  of  frequent  occurrence  in  the  nomenclature 
of  the  arms  of  the  sea.  The  color  of  sea-water  is  both  apparent 
and  real.  The  ajjparent  hue  is  often  due  to  reflection  from  the 
sky  ;  the  real  color  to  the  substances  in  solution.  Shallow  water 
is  commonly  f,'reeni.sh  ;  deep  water  a  dark  blue.  The  water  of 
the  Gulf  Stream  has  a  peculiar  blue  color  and  is  instantly  dis- 
tinguished from  the  lighter  colored  water  on  either  side.     The 


210  PHYSICAL   GEOGRAPHY 

phosphorescence  of  sea- water,  usually  observed  in  warm  regions, 
is  due  to  a  microscopic  organism,  Noctihica  miliaris,  that,  like 
the  common  firefly,  has  the  power  of  emitting  light.  At  times 
the  wake  of  a  vessel  seems  like  a  track  of  fire. 

"  Bulk  for  bulk,  ice  is  ligliter  than  water.  Solid  sea-ice  floats 
with  about  one-eighth  of  its  mass  above  the  surface.  If  it  con- 
tains air-bubbles,  however,  a  greater  proportion  is  out  of  water. 

"  In  a  few  instances  the  formation  known  as  anchor  ice  takes 
place.  It  results  from  the  freezing  of  fresh  water  at  the  bottom 
of  an  estuary  into  which  salt  water  flows.  The  ice  accumulates 
on  the  bottom  until  its  buoyancy  overcomes  the  force  with  which 
it  adheres  to  the  bottom ;  then  the  whole  mass  rises  to  the  surface. 
It  receives  its  name  from  the  fact  that  it  is  very  apt  to  begin 
forming  about  anchors  or  otlier  metallic  substances  lying  at 
the  bottom.  In  certain  cases  these  have  been  lifted  from  the 
bottom  and  floated.  In  some  instances  large  areas  of  anchor-ice 
have  become  suddenly  detached  from  the  bottom,  and  the  estu- 
ary, a  few  minutes  previously  free  from  ice,  becomes  filled  with 
sludge.     This  form  of  ice  is  also  called  ground-ice. 

*  The  formation  of  the  pack  is  sometimes  sudden  and  frequently 
violent.  The  crunching  from  side-pressure  is  so  great  that  not 
only  is  the  ice  piled  up  in  huge  blocks,  but  the  blocks,  often 
weighing  many  tons,  are  shot  up  into  the  air  ten  or  twenty  feet. 

'  The  difference  in  the  form  of  the  Greenland  and  the  south 
polar  icebergs  is  due  to  the  character  of  the  glaciers  from  which 
they  are  broken.  Antarctic  glaciers  are  derived  from  sheets  of 
land  ice  ;  Greenland  bergs,  on  the  contrary,  are  derived  mainly 
from  the  hummocky  ice  of  glaciers  that  flow  in  ravines.  It  is 
commonly  asserted  that  most  of  the  icebergs  floating  down 
through  Davis  Strait  come  from  Humboldt  Glacier.  As  a  matter 
of  fact  scarcely  a  single  one  comes  from  this  quarter  ;  they  nearly 
all  come  from  Disko  Bay. 

*A  breeze  of  two  miles  an  hour  throws  the  surface  of  still 
water  into  ripples  two  or  three  inches  broad  and  not  far  from  an 
inch  in  height.  The  slope  of  the  wave  is  rarely  the  same  on  both 
sides.  The  wind  pushes  the  crest  forward  so  that  the  front  of  the 
wave  is  considerably  steeper  than  the  back.  Large  waves  as  a 
rule  result  from  the  union  of  smaller  ones,  and  this  process  goes 
on  until,  finally,  the  accumulation  is  the  greatest  mass  that  the 
breeze  of  the  given  velocity  can  move. 


WAVES,    TIDES,    AND    CURRENTS  211 

'  Strictly  speaking,  it  is  a  matter  of  adhesion  rather  than  fric- 
tion, and  when  the  wind  blows  over  the  surface  of  still  water  the 
lower  surface  of  the  air  actually  remains  in  contact  with  the 
water.  In  a  stiff  gale  tlie  dragging  force  exerted  on  the  surface 
of  the  water  by  the  wind  amounts  to  a  little  more  than  one 
ounce  on  each  squai*e  yard  of  surface. 

"  The  effect  of  the  wind  is  to  push  their  crests  forward  rapidly, 
practically  flattening  them. 

'  A  stanch  vessel  with  her  head  to  the  tvind  need  fear  but  little 
from  the  waves.  The  latter  may  smash  everytliing  above  deck, 
but  the  hull  will  ride  tlie  waves  safely  so  long  as  they  do  not 
board  her.  Riding  so  that  the  waves  strike  broadside,  however, 
is  a  different  matter,  and  no  vessel  can  accomplish  it  without 
danger  of  foundering.  The  danger  from  waves  arises  not  so  much 
from  their  height  but  from  the  possibility  of  their  breaking  upon 
and  boarding  the  vessel.  Otherwase  a  ship  can  ride  waves  of  sixty 
feet  as  safely  as  those  of  six. 

"  In  the  use  of  oil  and  similar  substances  two  results  must  be 
studied — namely,  to  prevent  the  growth  of  waves,  and  to  prevent 
their  breaking.  In  the  great  majority  of  instances,  however,  the 
problem  before  the  sailing  master  is  to  prevent  the  breaking  of 
waves.  For  this  purpose  it  is  found  that  sperm  oil  and  oil  of 
turpentine  are  the  best.  In  use,  the  oil  is  poured  into  a  coarse 
canvas  sack  and  the  latter  is  floated  to  the  windward  of  the  ves- 
sel, being  held  in  position  by  any  convenient  outrigging.  The 
oil  oozing  through  the  canvass  spreads  raj)idly  over  the  surface  of 
the  water.  Instantly  the  waves,  though  they  may  run  high,  cease 
to  break.  The  following  from  the  log  of  the  Swedish  brigantine 
T)rott  is  one  of  a  great  many  similar  testimonials  gathered  dur- 
ing the  past  few  years  by  the  United  States  Hydrographic  Office  : 
"  I  had  seen  upon  the  pilot  chart  that  oil  had  been  used  with 
good  effect  in  calming  heavy  seas.  I  started  to  try  it  and  had  two 
bags  made  of  the  capacity  of  two  gallons  each.  These  bags  were 
stuffed  full  of  oakum,  and  then  one  gallon  was  poured  into  each, 
half  fish  oil  and  half  [X'troleum.  A  very  small  hole  was  cut  in 
the  bottom  of  each  Ijag  which  allowed  the  oil  to  drop  out  freely. 
One  of  these  bags  was  suspended  from  each  cathead,  just  out  of 
the  water,  and  the  result  was  simply  a  wonder  to  me,  so  much 
so  that  I  could  hardly  believe  my  senses.  No  more  seas  were 
shiijped  and  all  iiands  turned  to  secure  flic  main  hatchway  prop- 


213  PHYSICAL  GEOGRAPHY 

erly,  which  was  impossible  to  do  before  on  account  of  tlie  risk  of 
being  washed  overboard.  The  former  combers  were  now  great 
rollers  only,  not  a  sea  breaking  nearer  than  thirty  feet  from  the 
vessel.  The  crew  were  now  able  to  fnimp  out  the  ship  and  clear 
up  the  decks  in  perfect  safety.  About  11  p.m.  the  sea  broke  over 
the  starl)oard  side  and  smashed  in  one  of  the  boats,  but  this  was 
found  to  be  due  to  the  loss  of  one  of  the  oil  bags,  and  as  soon  as 
another  was  put  out  and  kept  supplied  with  oil  no  more  waves 
came  on  board." 

"  This  theory  of  the  tides  is  not  accepted  by  all  astronomers. 
See  Ap2yendix,  Table  VI. 

'^  At  Lady  Franklin  Bay,  Lieutenant  (now  General)  Greely 
observed  that  the  tide  came  from  the  north. 

'^  During  pleasant  weather  the  eddy  of  the  Maelstrom  is  hard- 
ly noticeable  during  slack  water,  or  at  the  time  of  neap  tides. 
When  the  flood  or  the  ebb  of  spring  tides  is  strong,  however,  the 
current  is  strong,  and,  wdth  a  hard  northwest  wind,  it  is  a  dan- 
gerous locality. 

"  According  to  Herschel  and  Carpenter  the  winds  themselves 
pile  up  the  waters  in  equatorial  latitudes,  thereby  bringing  about 
a  condition  of  inequilibrium.  Lieutenant  Maury  held  that  the 
difference  in  specific  gravity  between  the  saltier  waters  of  equa- 
torial and  the  fresher  waters  of  polar  regions  is  competent  to 
account  for  ocean  cui-rents.  That  each  is  an  important  factor 
cannot  be  denied. 

'*  Owing  to  the  turning  of  the  earth  on  its  axis,  a  point  on  the 
equator  ti-avels  25,000  miles  in  twenty-four  hours — a  speed  of 
about  1,000  miles  an  hour.  In  latitude  60°  it  is  only  half  as 
much.  Consequently  water  flowing  from  latitude  60°  toward  the 
equator,  every  point  of  which  has  a  greater  velocity,  has  a  ten- 
dency to  lag  behind. 

'"  The  velocity  varies  not  only  with  tlie  season,  but  also  with 
Mie  age  and  the  passage  of  the  moon — that  is,  the  variations  are 
yearly,  monthly,  and  daily.  The  velocity  is  greatest  during  sum- 
mer and  least  in  winter.  The  position  of  the  axis  of  the  stream, 
or  line  of  swiftest  flow,  changes  also  with  the  season.  An  adverse 
wind  will  retard  ;  a  favorable  wind  will  increase  its  velocity. 
A  quartering  wind  or  one  blowing  athwart  is  apt  to  push  some  of 
the  surface  water  out  of  the  track  of  the  stream,  at  the  same  time 
pushing  colder  water  into  it.     The  fact  that  Gulf  Stream  water 


WAVES,    TIDES,    AXD   CURREXTS  -^13 

is  occasionally  pushed  against  the  coast  has  more  than  once 
given  rise  to  the  statement  that  its  position  is  subject  to  change. 

''  Glaciers  and  glacial  action  have  also  had  much  to  do  with 
the  shaping  qi  surface  features  of  these  coasts.  The  coasts  of  Ire- 
land, Norway,  Alaska,  and  Chile  much  resemble  that  of  Maine. 
Their  general  outline,  however,  is  due  to  submergence  ;  with  the 
lowering  of  the  level  of  the  land,  the  waters  cover  the  valleys. 

'"  During  the  reign  of  Henry  VIII.  the  church  of  Reculver  stood 
at  the  distance  of  a  mile  from  the  shore,  but  the  sea  now  laves 
its  foundation  stones.  The  famous  Goodwin  Sands,  a  shoal  about 
twenty  square  miles  in  extent,  southeast  of  Kent,  was  formerly  a 
part  of  the  mainland.  In  the  twelfth  century,  during  a  severe 
storm,  this  area  was  washed  away  by  the  sea,  and  has  been  cov- 
ered with  water  ever  since.  The  channels  through  this  shoal 
shift  with  every  storm. 


CHAPTER  XII 
THE  ATMOSPHERE  AND  ITS  PROPERTIES  :     WINDS 

The  atmosphere,  or  air,  is  the  gaseous  substance  that 
forms  the  outer  envelope  of  the  earth.  It  rests  on  the 
land  and  the  Avater,  and  probably  penetrates  both  to  a 
considerable  distance.  Being  a  part  of  the  earth,  the 
atmosphere  partakes  of  all  the  general  motions  of  the  lat- 
ter, but  it  has  also  certain  movements  of  its  own,  and 
these  are  very  closely  connected  with  life  and  its  envi- 
ronment. 

The  air  is  not  a  simple,  or  elementary  substance  ;  as 
noted  on  p.  22,  it  is  a  mixture  of  several  elements.  The 
chief  constituents,  nitrogen  and  oxygen,  have  the  propor- 
tion of  about  four  parts  of  the  former  to  one  of  the  latter, 
and  the  proportion  does  not  change  materially.  The  re- 
maining constituents,  water  vapor,  carbon  dioxide,  and  float- 
ing matter  vary  greatly.  The  vapor  of  water  rarely  exceeds 
one  part  in  one  hundred  of  air.  It  is  nevertheless  a  most 
important  constituent,  for  it  is  in  this  form  that  the  water 
is  borne  from  the  sea  and  shed  upon  the  land.  The  floating 
particles  of  smoke,  dust,  and  other  matter  are  also  essen- 
tial, for  they  aid  materially  in  condensing  the  water  vapor. 

The  air  is  highly  elastic.  Stop  the  nipple  of  a  bicj'cle 
pump  and  push  the  piston  quickly;  note  what  occurs. 
Pressure,  therefore,  decreases  the  volume,  making  the  air 
denser.  When  the  pressure  is  relieved,  the  air  again 
expands  and  is  less  dense  or  rarefied}  Air  next  the 
ground  is  denser  than  that  al)ove,  because  of  the  pressure 

214 


THE    ATMOSPHERE   AXD   ITS   PROPERTIES     215 


or  weight  of  that  overlaviug  it.  The  density  decreases 
with  the  distance  above  the  sea;  at  an  altitude  of  two 
miles  the  density  is  only  two-thirds  that  at  sea-level.  At 
sea-level  a  cubic  foot  of  air  weighs  a  Uttle  more  than  one 
Troy  ounce. 

The  force  with  which  the  air  presses  upon  a  given  sur- 
face is  called  its  tension  ;  and,  practically,  the  tension  is 
a  form  of  expressing  its  pressure  ^  on  the 
rock  envelope.  At  sea-level,  the  column 
of  air  rests  upon  the  surface  with  a  press- 
ure of  about  fifteen  pounds  on  every  square 
inch,  or  a  little  more  than  a  ton  on  each 
square  foot  of  surface.  The  tension  varies 
slightly  in  different  latitudes,  being  a  little 
greater  near  the  tropics  than  elsewhere. 

It  is  most  convenient  to  estimate  the 
tension  of  the  air  by  obserA^ing  the  height 
of  a  column  of  mercury,  or  quicksilver,  that 
will  just  balance  it.  The  instrument  used 
for  this  purpose  is  called  a  barometer.  It 
consists  of  a  glass  tube  closed  at  one  end, 
and  filled  with  mercury ;  the  open  end  is 
placed  in  a  small  cup  filled  with  mercury. 
The  pressure  of  the  air  on  the  surface  of 
the  mercury  in  the  cup  keeps  the  column 
in  the  tube  in  place.  If  the  column  in  the 
tube  rises  it  signifies  that  the  pressure  of 
air  overhead  is  increasing ;  if  it  falls,  the 
pressure  is  decreasing.  The  weight  of  the 
mercury  in  the  tube  is  just  equal  to  that 
of  a  column  of  air,  having  an  equal  base,  and  the  two 
balance  each  other. 

The  atmosphere  is  warmed  pai'tly  by  the  direct  rays  of 
the   sun  and    partly  by  the  heat  radiated  from  the  earth. 


y 


THE  BAROMETER. 


216  PHYSICAL   GEOGRAPHY 

It  is  also  heated  by  compression  and  cooled  by  expan- 
sion. When  a  volume  of  air  is  compressed,  it  becomes 
greatly  heated.  Thus,  air  that  descends  from  higher  to 
lower  levels,  l)ecomes  heated  becanse  it  moves  into  a  re- 
gion where  the  density  and  tension  are  greater.  In  the 
same  way,  a  volume  of  rising  air  expands  and  is  cooled, 
because  it  goes  into  a  region  Avhere  the  tension  and  density 
are  less.  Heat  causes  the  air  to  expand  and,  bulk  for  bulk, 
warm  air  is  therefore  lighter  than  cold  air.^  If  a  volume 
of  air  is  warmed  from  freezing  temperature  to  that  of  in- 
tense summer  heat  its  volume  is  increased  nearly  one-fifth. 

The  temperature  of  the  air  varies  both  with  latitude 
and  with  altitude.  In  equatorial  latitudes  the  mean  tem- 
perature of  the  air  over  the  sea  is  not  far  from  32° 
(90°  F.)  ;  in  polar  regions  it  ranges  much  below  0°  (32°  F.). 
With  respect  to  altitude  there  is  a  fall  of  temperature  at 
the  rate  of  about  one  degree  for  every  three  hundred  feet 
of  ascent.  The  effect  is  very  noticeable  in  the  equatorial 
Andes.  At  the  base  of  tlie  mountains  the  heat  is  intense  ; 
at  an  altitude  of  ten  thousand  feet  the  air  is  mild  and 
pleasant ;  at  seventeen  thousand  feet  one  lives  in  a  region 
of  perpetual  snow. 

Movements  of  the  Atmosphere.— Like  the  waters 
of  the  sea,  the  air  is  everywhere  in  motiou.  The  move- 
ments are  both  general  and  local.  The  attraction  of  the 
sun  and  the  moon  undoubtedly  causes  atmospheric  tides 
something  hke  the  tides  of  the  sea.  Their  effects,  how- 
ever, are  very  slight,  and  practically  nothing  is  known 
about  them. 

Sensible  movements  of  the  air  are  called  ivinds,  and 
they  are  caused  by  changes  of  temperature.  When  the 
air  at  some  locality  or  other  is  heated  to  a  temperature 
higher  than  that  surrounding,  it  expands  and,  becoming 
lighter,  bulk  for  bulk,  it  is  pushed  upward  by  the  heavier 


THE   ATMOSPHERE   AXD    ITS    PROPERTIES     217 


air  that  flows  in.  lu  this  way  winds  originate.  Such 
movements  of  the  air  are  everywhere  taking  place,  and  it 
is  evident  that  they  a,re  examples  of  the  force  of  gravity. 

Equatorial  and  polar  regions  are  not  equally  heated. 
The  former  receives  the  almost  vertical  rays  of  the  sun ; 
the  latter  only  oblique  rays.  The  air  in  low  latitudes, 
therefore,  is  warmed  and  pushed  upwards  by  the  inflow  of 
cokler  air.  This  process  results  in  two  great  movements, 
namely  —  a  sur- 
face  floio  toward 
the  equator^  and 
upper  currents 
from  the  equato- 
rial toivard  po- 
lar 7'egions. 

But  the  colder 
air  comes  from 
the  regions  where 
the  speed  of  the 
earth's  rotation 
is  comparatively 
slow,  and  enters 
latitudes  where 
it  is  much  great- 
er ;  and  not  be- 
ing able  to  acquire  this  speed  at  once  it  lags  behind,  pro- 
ducing a  current  to  the  westward.  The  rising  current 
moves  into  a  region  in  which  the  speed  of  rotation  is  not 
so  great,  and  therefore  moves  eastward,  as  well  as  toward 
the  north. 

Winds  are  usually  named  according  to  the  direction 
from  which  they  come.  But  in  the  two  great  movements 
described  the  easterly  and  the  westerly  components  are 
much  more  noticeable  than  the  polar  and  equatorial  move- 


GHNERAL  MOVEMENTS  OF  THE  ATMOSPHERE. 


218 


PHYSICAL   GEOGEAPHY 


meiits.  For  this  reason  it  is  customary  to  recognize  three 
great  belts  of  winds — a  belt  of  equatorial  or  easterly,  be- 
tween two  zones  of  extra-tropical  or  westerly  winds.  These 
general  movements  are  very  strongly  marked  in  the  oceans, 
but  they  are  greatly  modihed  by  the  continents  ;  in  inland 
mountainous  regions  they  might  escape  notice  except 
through  long-continued  observations ;  in  the  great  lowland 
plains  they  are  more  regular. 

Trade  Winds. — The  surface  winds  that  flow  into  trop- 
ical regions  to  take   the   place   of   the   warm   air  that  is 


January. 


PREVAILING   WINDS   OF   THE   ATLANTIC. 


July. 


pushed  upward,  form  the  well-known  Trade  Winds.  What 
is  their  direction  in  the  northern  half  of  the  belt  ?  in  the 
southern  half  ?  Toward  the  centre  of  the  belt  they  are 
practically  strong,  steady  easterly  winds. 

The  zone  of  Trade  Winds  is  about  fifty  degrees  in  width. 
Its  position  is  not  stationary ;  it  swings  back  and  forth, 
north  and  south,  as  the  seasons  change.  In  the  Atlantic 
Ocean  the  shifting  of  the  belt  is  not  far  from  eight  or  ten 


THE   ATMOSPHERE   AA^D    ITS   PROPERTIES     219 

degrees ;  in  the  Pacific  it  is  sliglitl}'  greater.  The  belt 
reaches  its  northern  limit  in  early  autumn  ;  its  southern 
limit  in  early  spring.  The  winds  are  reguhir  and  constant 
the  year  round,  and  their  velocity  is  not  far  from  twelve  or 
fifteen  miles  an  hour. 

Formerly,  when  most  of  the  ocean  commerce  depended 
on  sailing  vessels,  these  winds  were  of  great  importance — 
hence  their  name.  A  vessel  entering  the  Trade  Wind 
belt  could  rely  on  steady  winds  with  but  little  interruption 
from  cyclones. 

Along  the  line  where  the  northerly  and  the  southerly 
components  of  the  Trade  AViuds  meet,  there  is  a  narrow 
belt  which  is  characterized  by  an  absence  of  steady  winds. 
This  belt  is  the  updraught  of  heated  air  and  is  called  the 
Equatorial  Calms,  or  Doldncuis.  This  calm  belt  is  scarcely 
more  than  two  or  three  hundred  miles  in  breadth.  Some- 
times vessels  were  becalmed  several  weeks  in  crossinsf  it. 
The  wind  comes  only  in  fits  and  puffs,  or  Avith  an  occa- 
sional thunderstorm  of  great  violence. 

Prevailing  Westerlies. — The  air  that  flows  from  equa- 
torial regions  as  an  upper  current,^  in  temperate  latitudes 
sinks  to  the  surface  and  becomes  a  belt  of  westerly  winds, 
now  generally  called  the  Prevailing  Westerlies  ;^  what  is 
their  direction  in  the  Northern  Hemisphere  ?  in  the 
Southern  Hemisphere  ?  Like  the  Trade  Winds  both  belts 
move  northward  and  southward  with  the  changes  of  the 
seasons. 

In  the  Northern  Hemisphere  the  Prevailing  Westerlies 
are  neither  so  strong  nor  so  steady  as  the  Trade  Winds, 
and  in  higher  latitudes  they  often  give  way  to  winds  of 
northerly  origin.  On  the  coast  of  the  Gulf  of  Mexico  the 
Prevailing  Westerlies,  in  the  summer  season,  are  reinforced 
by  Trade  Winds  which  are  deflected  by  the  highlands  of 
Mexico.     The  resulting  winds  sweep  up  the  Mississippi 


220  PHYSICAL   GEOGRAPHY 

Valley  and  thence  turn  across  the  Atlantic,  carrying  with 
thorn  a  great  deal  of  the  moisture  that  supplies  the  East- 
(>rn  United  States  with  rain. 

Til  the  Southern  Hemisphere,  the  Prevailing  Westerlies 
are  best  known  as  the  Roaring  Forties.  They  cover  a 
very  broad  stretch  of  sea,  and  they  furnish  an  excellent 
illustration  of  the  theoretical  movement  of  the  constant 
winds.  When  the  trade  route  between  Europe  and  the 
East  Indies  lay  around  the  Cape  of  Good  Hope,  the  Eoar- 
ing  Forties  were  a  very  important  factor,  as  the  sailing 
master  could  depend  on  a  twenty  or  thirty  knot  breeze  the 
year  round.  It  was  then  a  common  practice  for  vessels 
bound  for  Australia  or  New  Zealand  to  continue  the  route 
eastward  and  return  by  way  of  Cape  Horn.  Trace  this 
route  on  a  globe. 

The  descent  of  the  upper  currents  to  the  sm-face,  which 
is  the  origin  of  the  Prevailing  Westerlies,  is  marked  by 
calm  belts — the  Calms  of  Cancer,  and  the  Calms  of  Capri- 
corn. Like  the  zones  of  constant  winds  the  calm  belts 
also  shift  north  and  south  with  the  season.  They  are  in- 
terrupted by  the  continents  and  are  scarcely  to  be  noticed 
within  a  hundred  miles  of  their  shores.  The  Calms  of 
Cancer  are  the  well-known  "  Horse  Latitudes."  ^  The  Calms 
of  Capricorn  are  the  Avider  and  more  continuous  of  the  two 
calm  belts. 

Monsoons. — Along  many  coasts  having  a  southerly  or 
a  southwesterly  exposure  the  summer  winds  have  a  direc- 
tion nearly  opposite  those  of  the  winter  season  ;  that  is, 
about  half  the  year  they  blow  from  the  sea ;  the  remaining 
half  toward  the  sea.  These  winds  are  called  monsoons.'' 
Two  causes  operate  to  give  these  winds  their  peculiar 
character — in  some  instances  singly ;  in  others  together. 

In  the  first  place,  any  great  body  of  land  is  apt  to  be- 
come much  warmer  than  the  sea  in  summer  and  colder  in 


222  PHYSICAL  GEOGRAPHY 

Aviuter.  As  a  result,  during  summer  there  is  an  updraught 
of  warm  air  pushed  upward  by  the  inflow  of  sea  air.  In 
winter  the  conditions  are  reversed  ;  cold  air  flows  from  the 
land  to  the  sea.  In  other  instances,  a  region  may  be  so 
situated  that  it  is  in  the  southeast  Trade  Winds  at  one 
part  of  the  year,  and  in  the  northeast  part  the  remainder. 
The  monsoons  of  the  Mexican  coast  are  probably  due 
to  this  cause. 

The  most  remarkable  monsoons,  however,  are  those  of 
the  Indian  coast.^  From  April  to  October  the  southerly 
half  of  the  belt  of  Trade  Winds  reaches  far  inland,  pouring 
a  deluge  of  rain  upon  the  land.  During  the  rest  of  the 
year,  on  the  contrary,  the  southerly  part  of  the  belt  has 
reached  southward,  and  the  northerly  half  extends  consid- 
erably bej'ond  the  coast,  parching  the  land  and  withering 
vegetation.  The  tremendous  updraught  of  warm  air  aids 
materially  in  giving  strength  to  these  winds.  The  "  break- 
ing" or  change  of  the  monsoon  is  usually  attended  b}-  a 
number  of  terrific  storms. 

Along  the  Gulf  coast  of  the  United  States  the  deflected 
Trade  Winds  of  the  summer  season,  noted  on  p.  219,  that 
flow  up  the  Mississippi  Valley  are  rejolaced  by  Prevailing 
Westerlies  that  are  turned  doivn  the  valley.  These  winds 
may  be  regarded  as  monsoons,  but  they  are  neither  so 
regular  nor  so  strong  as  the  Indian  monsoons. 

Day  and  Night  Breezes.— The  difference  between  the 
temperature  of  day  and  night  is  sufficiently  great  to  result 
in  strongly  marked  local  winds.  Thus,  along  the  coasts, 
especially  warm  regions,  the  updraught  of  the  land  causes 
a  stiff  on-shore  wind  during  the  day,  while  at  night  the 
air  over  the  land,  being  more  quickly  chilled,  flows  down 
the  slopes  toward  the  sea.^  Thus  there  results  a  sort  of 
daily  monsoon,  or  day  and  night  local  wind.  Coast  fisher- 
men  frequently  take  advantage   of  such  winds;  they    go 


I 


THE   ATMOSPHERE   AND   ITS   PROPEKTIES     223 

out  in  the  morning  with  an  off-shore,  and  return  at  night 
with  an  on-shore  breeze. 

Similarly,  in  mountainous  countries  the  air  upon  the 
higher  slopes  is  commonly  heated  and  cooled  more  rapidly 
than  in  the  valleys.  As  a  result  there  is  often  a  strong 
wind  blowing  icjj  the  valley  by  day,  and  flowing  downward 
at  night.  3Iounfcun  valley  loinds  of  this  character  are  very 
common  in  almost  every  rugged  countr}'.  Which  is  the 
better  indication  of  the  general  direction  of  the  wind — that 
noted  at  the  ground,  or  the  movement  of  the  clouds  ? 

Local  and  Variable  Winds. — There  are  many  winds 
occurring  at  irregular  intervals  that  are  confined  each  to  a 
particular  locality.  In  most  instances  these  winds  are 
confined  to  desert  regions  and  arid  lands,  or  else  they  re- 
sult from  the  proximity  of  the  latter.  Almost  always  they 
are  very  "  dry  "  winds. 

Thus,  the  Northers  of  Texas  and  Mexico  are  cold  winter 
winds  of  several  days'  duration  that  blow  from  the  high- 
lands of  the  Plateau  region.  The  Chinook  and  Santa  Ana 
wdnds  of  the  western  highlands  of  the  United  States  are 
descending,  and  therefore  warm  winds  blowing  from  arid 
regions  upon  fertile  lands.  In  southern  Europe  they  are 
called  Foehn  winds.^*^  The  Pamperos  are  similar  winds 
flowing  from  the  cold  slopes  of  the  Andes  over  the  arid 
pampas  of  Argentina.  The  Punas  of  the  Peruvian  table- 
lands are  of  the  same  nature. 

In  the  vicinity  of  the  African  desert  are  the  famous 
Mistral  and  the  Etesian  winds,  both  blowing  from  the 
snow-clad  Alpine  ranges  toward  the  desert,  while  the 
Sirocco,  like  the  Chinook,  is  a  hot  wind  that  in  summer 
blows  from  the  desert.  The  Harmattan  is  a  warm  winter 
wind,  blowing  from  the  desert  to  the  Guinea  coast.  Aside 
from  these  there  are  several  winds  peculiar  to  desert  re- 
gions.    Chief  among  them  is  the  Simoon,  a  fierce  blast  of 


224  PHYSICAL   GEOGRAPHY 

hot  air  and  rock  waste,  that  neither  man  nor  beast  can  face. 
It  is  common  both  in  the  Okl  World  and  the  American 
deserts.  A  mikler  form  of  this  wind  along  the  lower  Nile 
valley  is  called  the  Khamsin.  Classify  these  winds  as 
either  hot  blasts  froa  the  desert,  or  colds  winds  bloAving 
into  it. 

The  most  interesting  of  all  desert  winds,  however, 
are  the  sand  whirls.  These  occur  in  the  morning  when 
the  air  is  still — never  Avhen  wind  is  blowing.  Under  a  hot 
sun  the  air  next  the  earth  becomes  considerably  heated, 
having  a  high  temperature.  Above  the  ground  the  air  is 
cooler  at  the  rate  of  one  degree  F.  for  every  three  huudi'ed 
feet.  Thus  there  is  formed  the  very  unstable  condition 
of  a  layer  of  heavy,  cold  air  on  a  surface  stratum  that  is 
much  lighter.  Such  a  condition  cannot  last  long,  and 
sooner  or  later  some  slight  disturbance  or  other  starts  a 
slender  column  of  air  upward. 

Immediately  the  stratum  of  cold  air  begins  to  settle, 
and,  as  it  descends,  it  forces  the  warm  air  upward  through 
the  self-made  passage.  The  ascending  column  begins  to 
whirl,  and  soon  its  motion  is  rajjid  enough  to  carry  with  it 
a  cloud  of  dust  and  fine  rock  waste. 

As  a  rule  these  whirls  begin  when  the  sun  is  two  or 
three  hours  high,  and  continue  until  the  wind  begins  to 
blow.  The  latter,  by  mixing  the  warm  air  with  the  cold, 
prevents  their  formation  until  a  calm  again  begins.  Oc- 
casionally such  whirls  develop  into  very  vigorous  "  sand 
spouts." 

Physiographic  Effects  of  Winds.— As  an  agent  in 
wearing  away  the  surface  of  the  land,  the  wind  acts  in  dif- 
ferent ways.  It  may  alter  the  chemical  composition  of  the 
rock  with  which  it  comes  in  contact.  It  may  carry  minute 
particles  that  cut  away  softer  material.  It  may  transport 
material  from  one  place  to  another.     The  chemical  action 


THE   ATMOSPHERE   AND   ITS   PROPERTIES     225 


of  air  is  due  mainl}'  to  the  water  and  carbon  dioxide  which 
it  contains.  It  is  manifested  in  the  gradual  crumbling  of 
many  rocks,  when  the  latter  are  exposed  to  the  air.  The 
rocks  most  affected  are  certain  iron  ores  and  granite  rocks. 
Dry  air  may  affect  rocks  by  chemically  withdrawing  the 
moisture  they  contain  ;  moist  air  niay  affect  other  kinds  by 
chemically  imparting  Avater  to  them.  In  either  case  the 
rock  sooner  or  later  crumbles. 

The  impact  of  minute  particles  carried  by  the  wind  is 
especially  noticeable  in  the  western  highlands.    In  regions 


SAM)  i;l-..\  FHN    ROCK 


where  sand  winds  are  prevalent  the  surfaces  of  the  hardest 
rocks  are  worn,  channelled,  and  polished  from  this  cause. 
Many  of  the  "  needles  "  or  rock  spires  of  this  region  liave 
been  sculptured  into  fantastic  forms  by  feolian  or  wind- 
bl(j\vn  rock  waste." 

The  transporting  power  of  the  wind  is  coiifiucd  chiotly 
to  sea-sh<jres  and  regions  unprotected  by  vegetation. 
AVhy?     The  wave-formed  islands  and  barrier  beaches  of 


>50 


riTYSIOAL   GEOCtRAPHY 


the  Atlantic  and  Gulf  coast  Lave  foundations  of  sea  sedi- 
ments, but  the  above-water  part  consists  of  wind-blown 
material.  The  sand-dunes  of  sea  and  lake  shores  are  ex- 
cellent illustrations,  and  in  regions  swept  by  monsoons  the 
dunes  travel  seaward  during  one  season  and  landward  the 
other.  A  Avave  of  sand  about  a  mile  long  and  seventy  feet 
high  at  one  time  inundated  a  part  of  Cape  Henlopen.^^ 

Between  tlie  silt  brought  down  by  the  Colorado  River, 
and  the  fierce  winds  of  that  region,  the  Gulf  of  California 


DUNES   OF   SAND 

has  been  cut  in  twain,  and  most  of  the  severed  portion 
filled  with  rock  waste  to  a  height  now  considerably  above 
sea-level ;  indeed,  all  through  this  region  dunes  are  con- 
stantly forming,  shifting,  and  re-forming.  In  western 
Nebraska,  wdiere  the  rainfall  is  not  sufficient  to  grow  pro- 
tective vegetation,  dunes  are  common. 

Very  notable  examples  of  the  transporting  power  of 
wind  occur  in  China.  In  the  basin  of  the  Hoang  River 
there  are  aeolian  deposits  covering  many  thousand  square 
miles  to  a  depth  of  several  hundred  feet.     These  deposits, 


THE    ATMOSPHERE  AND    ITS    PROPERTIES     227 

called  loess — from  a  German  word  meaning  "  loose  " — are 
thought  to  come  from  the  desert  region  to  the  westward. 
In  many  places  the  rivers  have  cut  their  channels  through 
the  loess,  and  the  latter  not  only  colors  the  water  of  the 
river,  but  imparts  a  yellow  tint  to  the  sea  into  which  it 
flows. 

J^olian  deposits  have  filled  most  of  the  valleys  of  the 
Basin  Region  of  the  western  highlands.  The  ranges  stand 
out  in  bold  relief  from  an  ocean  of  level  rock  waste.  Many 
of  the  valleys  of  the  Eocky  Mountains  have  been  filled  and 
levelled  in  the  same  manner. 

QUESTIONS  AND  EXERCISES.— Devise  or  describe  an  experi- 
ment to  show  that  air  has  weight  ;  show  that  it  is  elastic  ;  show 
that  heating  a  volume  of  air  causes  it  to  expand  ;  using  a  bicycle 
pump,  show  that  compressing  air  warms  it. 

What  is  the  prevailing  direction  of  the  wind  in  the  locality  in  which 
you  live?  Consult  the  records  of  the  nearest  weather  station  and  com- 
pare the  number  of  days  of  westerly  winds  with  the  number  in  which 
the  wind  is  from  other  directions. 

The  tropical  calm  belts  are  regions  of  descending  air-currents  ■.  is  the 
air  apt  to  be  chilled  or  warmed  by  this  movement  ? 

Read  Stedman's  poem,  "  The  Simoon,"  and  compare  it  with  the 
description  in  any  standard  cyclopedia. 

Why  are  northerly  winds  apt  to  be  cold  ? 

Explain  the  manner  in  which  street  whirlwinds  are  formed 

Note  any  instance  of  the  physiographic  effects  of  winds  in  the  lo- 
cality with  which  you  are  best  acquainted  ;  prepare  a  description  of  it. 

In  what  way  do  the  general  winds  affect  the  temperature  of  the 
earth  ? 

Note  any  examples  in  which  winds  accomplish  work  that  has  an 
economic  value 


COLLATERAL    READING   AND   REFERENCE. 

U.  S.  Coast  Sukvky.— Atlantic  Coast  Pilot  Chart,  for  March 
and  September,  or  Fehniary  and  Auf?ust — any  year. 
Lk  Contk.  — Elements  of  (ieolof^y,  I)p.  \-H. 


238  PHYSICAL   GEOGRAPHY 


NOTES 

'  At  a  heif?ht  of  fifteen  thousand  feet  the  air  is  so  rare  that 
breathiu}^  is  labored  and  the  pulsations  of  the  heart  are  very 
rapid.  Climbing  becomes  difficult  and  any  form  of  exertion  is 
very  wearying.  Water  boils  at  about  85°  (185"  F.),  a  temperature 
so  low  that  it  is  difficult  to  cook  vegetables  by  boiling. 

'  Approximately  the  pressure  is  one-half  a  pound  for  every 
inch  in  the  height  of  the  column  of  mercury.  At  the  level  of  the 
sea,  the  height  of  the  barometer  varies  usually  between  39  and 
30.4  inches. 

'  It  is  well  to  bear  in  mind  that  the  common  expression,  "hot 
air  rises,  because  it  is  lighter,"  is  not  strictly  correct.  The  hot 
air  does  not  rise  ;  it  is  pushed  upwards  and  floated  on  the  surface 
of  the  heavier  air. 

*The  height  to  which  the  updraught  rises  before  it  turns 
toward  the  pole  is  not  known,  except  in  two  or  three  instances. 
On  the  Island  of  Hawaii,  the  Trade  Winds  reach  an  altitude 
of  about  twelve  thousand  feet.  Above  this  elevation  the  winds 
have  almost  an  opposite  direction  ;  they  are  the  winds  that,  a 
few  degrees  farther  north,  descend  to  become  the  Prevailing 
Westerlies. 

^  The  Prevailing  Westerlies  are  also  called  return-trades,  anti- 
trades, and  counter-trades.  The  name  here  used  is  now  com- 
monly emjjloyed  in  meteorology. 

"  Many  years  ago,  when  most  of  the  foreign  carriage  was 
effected  by  sailing  vessels,  there  was  a  brisk  trade  in  horses 
between  the  ports  of  the  New  England  States  and  the  West 
Indies,  nearly  all  the  horses  used  in  the  latter  country  being 
obtained  from  New  England.  Frequently  the  vessels  were  be- 
calmed in  this  belt,  and  it  became  necessary  to  throw  overboard 
half  the  number  of  horses,  in  order  to  save  the  remaining 
animals. 

'  The  name  is  derived  from  a  Malay  word,  meaning  "season." 

*  On  account  of  its  inland  position.  Central  Asia  is  marked  by 
great  extremes  of  temperature.  During  summer  its  vast  deserts 
are  almost  like  a  furnace,  and  the  updraught  of  heated  air  is  so 
enormous  that  it  causes  atmospheric  disturbances  two  thousand 
miles  away.     In  winter  the  dry  air  is  chilled  many  degrees  below 


THE   ATMOSPHERE   AND   ITS   PROPERTIES    239 

that  of  the  warm  sea-air,  and,  being  correspondingly  heavier, 
tlows  outward  toward  tlie  ocean.  No  otlier  body  of  land  pos- 
sesses the  qualities  requisite  to  produce  monsoons  that  compare 
with  those  of  Asia. 

"  A  similar  movement  of  air  is  noticeable  in  many  large  caves 
— especially  those  that  have  openings  at  different  levels.  In  the 
daytime  air  in  the  cave  is  usually  colder  than  that  outside, 
while  at  night  it  is  w^armer.  As  a  result,  at  night  there  is  a 
strong  in-draught  of  colder  air  at  the  lower  entrance,  and  an  up- 
draught  at  the  higher  opening.  In  the  daytime  these  move- 
ments are  reversed. 

'"  These  three  names  are  applied  to  winds  that  have  certain 
principles  in  common.  Warm,  moist  air  is  pushed  up  the  side  of 
a  mountain-range  ;  being  cooled  either  by  its  own  expansion,  or 
by  contact  with  the  colder  mountain  top,  its  moisture  is  con- 
densed ;  the  air  then  descending  on  the  other  (or  ijossibly  the 
same)  side  warms  very  rapidly  by  its  own  compression.  The 
effect  is  very  marked  ;  snow  disappears  very  rapidly — hence  the 
popular  name  "snow-eaters."  The  descending  air  is  not  only 
warm,  but  it  is  so  dry  that  in  summer  it  withers  vegetation. 
The  Chinook  wind  gets  its  name  from  a  locality  in  Oregon, 
whence  it  seemed  to  come,  but  the  name  is  now  applied  to  warm 
winds  that  How  from  the  Rocky  Mountains  out  on  the  plains  to 
the  East.  Following  a  blizzard,  it  quickly  melts  the  snow  that 
covers  the  scanty  feed  of  the  cattle  herds.  The  Santa  Ana  is  a 
hot  wind  common  in  southern  California  and  Mexico. 

"  Some  years  ago  the  author  left  an  octagonal  steel  drill  in  an 
upright  position  exposed  to  the  full  sweep  of  a  desert  wind.  Six 
months  afterward  its  angles  had  been  almost  obliterated  by  the 
impact  of  rock  waste.  The  telegraph  poles  in  these  regions  are 
frequently  cut  in  two  by  the  wind-blown  rock  waste, 

"  It  is  likely  that  a  fire,  which  in  1828  burned  off  the  vegeta- 
tion protecting  the  ridge,  was  responsible  for  starting  this  dune  on 
its  travels.  In  184"),  (leneral  Joseph  E.  Johnston,  then  a  govorn- 
iiient  engineer,  noticed  that  north  winds  were  very  actively  at 
work  in  picking  up  sand  from  the  seaward  face  of  tlie  dune  and 
carrying  it  over  the  crest  to  the  landward  side.  Little  by  little 
the  wave  of  sand  overwhelmed  a  strip  of  pine  barrens  and  filled 
a  salt  marsh  beyond.  Tiien  it  advanced  upon  a  heavy  growth  of 
timber  and,  in  time,  covered  all  but  the  tallest  trees,  killing  them 


530  PHYSICAL   GEOGRAPHY 

as  effectually  as  though  they  had  been  swept  by  fire.  As  the 
years  passed  by  the  wave  steadily  advanced,  and  the  wind  began 
to  unciovei'  the  buried  surface  in  the  rear.  First  the  strip  of 
pine  barrens  re  api)oar(>d,  and  tlien  the  salt  marsh  was  cleaned 
out  and  promptly  reclaimed  by  the  tide.  Even  the  pine  barrens 
began  to  show  signs  of  life  and  a  growth  of  young  trees  sprang 
up.  Within  the  past  few  years  the  advancing  sand  has  begun 
to  uncover  the  forest,  and  a  border  of  dead  trees  now  flanks  the 
rear  slope.  Near  the  eastern  end  of  the  dune  is  Cape  Henlopen 
light-house.  A  straggling  ridge  of  the  wave  entered  the  yard, 
covered  up  the  oil-house  and  the  garden,  and  then  took  posses- 
sion of  the  keepers  cottage.  The  Government  acknowledged 
its  inability  to  cope  with  the  dune  by  erecting  a  new  cottage  on 
the  other  side  of  the  tower. 


CHAPTER  XIII 

THE     MOISTURE     OF    THE    ATMOSPHERE  .     SEASONAL 
AND  PERIODICAL  DISTRIBUTION   OF  RAINFALL 


The  Tapor  of  water  mingled  with  the  atmosphere,  iu  a 
way,  may  be  considered  a  part  of  it;'  but,  if  all  the  other 
constituents  were  absent,  the  water  vapor  would  exist  as  an 
atmosphere  in  itself,  and  its  movements  would  be  the  same 
practically  as  those  of  the  winds. 
But  while  the  proportion  of  oxygen 
and  nitrogen  of  the  atuiosphere  do 
not  perceptiblj"  varj^  that  of  water 
vapor  is  subject  to  rapid  changes. 
The  amount  present  depends  on  one 
thing  only — temperature.  With  a 
high  temperature  there  may  be  a 
great  deal  of  vapor  mingled  with  the 
air  ;  with  a  low  temperature  there 
can  be  but  little. 

Changes  in  humidity  are  usually 
apparent  to  the  sense  of  feeling,  and 
one  readily  learns  the  difference  be- 
tween moist  and  dry  air.'^  In  many 
instances  they  may  be  forecast  by 
observing  the  clouds.  If  the  latter 
form  rapidly,  or  if  small  patches  of 
cloud  increase  iu  size,  the  humidity 
is  increasing.  On  the  contrary,  if 
the  cloud  area  is  becoming  smaller,  it  is  highly  probable 
that  the  humidity  is  decreasing. 

231 


Till-    HYGROMETF-R. 


333  PHYSICAL  GEOGRAPHY 

Tlie  anioimt  of  moisture  is  determined  iii  various  ways 
Most  commouly  the  Ii)j(jronieter,  an  instrument  employed  to 
measure  the  amount  of  moisture,  consists  of  two  thermom- 
eters, the  bulb  of  one  being  covered  with  a  single  thickness 
of  wet  cloth.  If  the  air  be  dry,  the  water  that  saturates 
the  cloth  evaporates  rapidly  and  chills  the  bulb,  so  that 
the  reading  of  the  thermometer  is  several  degrees  lower. 
If  the  air  is  moist,  on  the  other  hand,  very  little  evaporates, 
and  the  difference  in  the  reading  of  the  thermometers  is 
very  slight.  From  the  difference  in  the  readings  of  the  two 
thermometers  the  amount  of  moisture  may  be  calculated. 

Dew  Point. — Table  VII.,  Appendix,  shows  the  amount 
of  water  vapor  there  may  be  in  the  air  at  various  tempera 
tures.-  With  the  thermometer  at  66°  F.,  for  instance, 
there  may  be  seven  grains  in  each  cubic  foot  of  atmos- 
phere. There  might  be  less,  but  there  can  be  no  more ; 
if  more  be  added  it  would  immediately  condense — that  is, 
change  to  rain  or  snow.  From  this  table  find  whether  or 
not  there  may  be  vapor  in  the  air  when  the  temperature  is 
below  freezing-point  of  water.  Compare  the  amount  at 
70°  F.  and  90°  F.  Learn  the  temperature  at  the  time  of 
recitation,  and  find  the  amount  of  moisture  there  may  be. 
What  is  the  general  law  shown  in  this  table,  so  far  as  tem- 
perature and  the  percentage  of  moisture  are  concerned  ? 

When  all  the  vapor  that  can  exist  at  a  particular  tem- 
perature is  present,  the  air  is  said  to  be  saturated  or  at  the 
deic-jooint.^  This  condition  is  unusual,  however,  except 
when  rain  is  falling ;  generally  the  amount  present  is  con- 
siderably less  than  that  required  for  saturation.  From  the 
amount  present  one  may  easily  compute  the  relative  hu- 
midity ;  thus,  if  half  the  quantity  required  to  saturate  the 
air  is  present,  the  relative  humidity  is  fifty  per  cent.  What 
is  meant  when  the  relative  humidity  is  eighty  per  cent.  ? 
If  the  amoimt  is  near  the  dew-point,  the  air  is  moist ;  if 


THE   MOISTURE   OF   THE   ATMOSPHERE    233 

the  relative  liumidity  is  low,  it  is  dry.  Air  that  is  moist 
at  a  given  temperature  maj  feel  very  dry  at  one  that  is 
higher,  even  though  no  more  moisture  is  present. 

Latent  Heat  of  Evaporation. — Water  is  changed  to 
vapor  by  heat.  When  water  boils  it  reaches  the  tem- 
perature at  which  it  begins  to  change  rapidly  to  steam. 
No  matter  how  tierce  the  heat  may  be,  the  water  (unless 
it  is  confined  under  pressure)  gets  no  hotter,  and  the  steam 
given  ofT  has  a  temperature  no  higher  than  that  of  the 
boiling  water. 

All  this  heat  is  absorbed  in  the  work  of  changing  the 
Avater  to  steam,  and  it  is  called  the  latent  heat  of  steam.  It 
has  not  been  lost,  however ;  it  is  merely  stored-up  energy. 
It  is  retained  just  so  long  as  the  water  remains  in  the  form 
of  vapor ;  it  is  given  out  the  moment  the  vapor  is  con- 
densed, or  changes  to  a  liquid. 

This  property  of  water  is  one  of  the  greatest  importance, 
for,  as  will  be  shown,  it  is  a  chief  factor  in  the  atmospheric 
disturbances  called  storms.  The  amount  of  heat  thus  ren- 
dered latent  is  very  great.  For  every  pound  of  water  con- 
verted to  steam,  as  much  heat  is  required  as  would  raise 
nearly  half  a  ton  of  water  one  degree  F. 

Dew. — Dew  is  the  moisture  that  gathers  on  the  ground 
after  sundown.  Both  the  air  and  the  ground  lose  a  part 
of  their  heat.  The  latter  cools  more  rapidly,  however, 
and  fiiiully  the  layer  of  air  next  the  ground  is  chilled  be- 
low the  dew-point.  When  this  occurs,  the  excess  of  vapor 
in  the  form  of  minute  drops  gathers  on  the  grass  and  on 
other  objects  jicar  the  ground.  The  moisture  that  gathers 
on  the  outside  of  a  glass  of  iced  water  is  an  exam])k\ 

Dew  does  not  always  form  at  night,  and  for  this  there 
are  several  reasons.  A  stiif  breeze  may  keep  the  air 
thoroughly  mixcnl,  and  tliereby  prevent  any  part  of  it 
from  being  chilled  to  the  dew-point.    The  air  may  contain 


234  PHYSICAL   GEOGRAPHY 

so  little  vapor  that  a  fall  of  fifteen  or  twenty  degrees  does 
not  bring  the  temperature  to  the  de\v-]joint.^  A  cloudy 
sky,  especially  if  the  clouds  hang  low,  prevents  the  radia- 
tion of  heat,  and  the  formation  of  dew.^ 

The  amount  of  moisture  in  the  air  varies  much.  In 
tropical  regions,  especially  those  near  the  sea,  the  amount 
is  proportionately  very  great.  Sometimes  it  is  so  near 
the  point  of  saturation  that  the  air  becomes  hazy.  In 
such  regions  dew  forms  copiously.  In  tem2:)erate  latitudes 
the  amount  is  much  less  than  in  tropical  regions. 

In  the  California  and  Sound  valleys,  where  there  are  no 
summer  rains,  the  fall  of  dew  in  early  summer  is  excessive, 
and  to  a  great  extent  the  grain  crop  is  dependent  upon  it. 
The  same  phenomenon  occurs  in  most  mountain  valleys. 

If  the  temperature  of  the  dew-point  be  lower  than  0° 
(32°  F.),  the  moisture  may  pass  immediately  into  the  crys- 
talline form,  frost.  Sometimes  the  minute  frost  crystals 
form  in  the  air,  but  usually  they  accumulate  on  the  grass, 
the  leaves,  and  other  objects  near  the  ground.  Sometimes 
the  frost  is  simply  frozen  dew.  Except  at  considerable 
altitudes  frost  does  not  occur  in  tropical  regions.  In  tem- 
perate latitudes  it  may  occur  at  any  time  between  late  fall 
and  spring.  Late  spring  frosts  are  apt  to  occur  after  fruit- 
trees  have  budded,  and  they  are  therefore  commonly  known 
as  killing  frosts.  The  cold  Avave  that  follows  a  spring  storm 
is  very  apt  to  lower  the  temperature  to  the  freezing-point, 
and  if  the  air  be  moist,  a  killing  frost  commonly  occurs. 
Fortunately  its  occurrence  usually  can  be  predicted. 

Clouds. — When  the  temperature  falls  so  low  that  a  part 
of  the  vapor  is  condensed,  the  latter  does  not  at  first 
gather  into  large  drops  ;  on  the  contrary,  the  drops  are  so 
minute  that  they  float  in  the  air.  This  floating  mist  of  the 
air  is  called  fog  or  cloud,  according  as  it  is  at  the  surface 
of  the  earth  or  high  in  the  air. 


THE   MOISTURE   OF   THE   ATMOSPHERE    235 


Nearly  always  the  air  is  filled  Avitli  dust-motes  and  other 
floating  matter,  and  much  of  the  condensing  vapor  gathers 
on  these.  Not  only  do  the  dust-motes  form  a  lodgement 
for  the  condensing  vapor,  but  they  cool  more  rapidly  than 
the  air,  and  thereby  quicken  the  process  of  condensation. 
Floating  matter  in  the  air  thus  becomes  an  active  agent  in 
cloud  formation.  The  cooling  of  the  air  below  the  dew- 
point,  however,  is  the  essential,  and  this  may  occur  in 
several  ways.  Thus,  when  a  mass  of  air  is  pushed  upward, 
not  only  is  it  chilled  by  going  into  a  cooler  position,  but 
it  is  also  cooled  by  its  own  expansion.  It  is  probable 
that  the  greater  amount  of  cloud  is  formed  in  this  manner. 
Thus,  in  equatorial  regions, 
where  there  is  a  constant 
up-draught  of  warm,  moist 
air,  there  is  a  perpetual 
cloud-belt. 

The  intrusion  of  warm 
winds  into  cold  regions,  or 
of  cold  winds  into  warm  re- 
gions, is  also  a  common 
cause  of  fog  and  cloud.  If 
the  intruding  wind  is  at  the  surface  of  the  earth  fog 
results ;  if  at  a  considerable  elevation  cloud  is  formed. 
The  fogs  and  cloud  banks  so  common  off  the  coast  of  New- 
foundland are  formed  in  this  way. 

Whenever  a  warm  sea- wind  blows  against  a  high  moun- 
tain-slope, a  part  of  tlu;  air  is  driven  up  the  slope,  and, 
some  of  its  moisture  being  condensed,  cloud  is  formed. 
Almost  always  high  mountain-crests  near  the  ocean  are 
shrouded  in  clouds,  and  not  infrequently  a  cloud  banner 
streams  from  the  leeward  side  of  a  high  jnjak.® 

Clouds  usually  take  cliara(;teristic  forms,  and  these  are 
governed  mainly  by  the  presence  or  absence  of  w  iud,  or  by 


CIKKO-STKATUS   CLOUDS 


530 


PHYSICAL  GEOGRAPHY 


their  height.  Cirrm  clouds  are  light  and  feathery  in  ap- 
pearance and  coniinonly  white  in  color.  These  clouds  take 
various  forms.  When  they  are  flaky  or  fleecy  they  are  the 
"  mackerel"  clouds  heralded  by  sailors  as  forecasters  of  fine 
weather;  but  cirrus  " streamers"  are  frequently  found  as 
an  advance  indication  of  an  approaching  cyclone.  Often 
the  patches  of  cirrus  cloud  are  ranged  in  parallel  strips ; 
and  occasionally  they  radiate  like  the  spokes  of  a  wheel. 


CUMULUS   CLOUDS 


Commonly  their  altitude  is  between  five  and  ten  miles. 
On  account  of  their  great  height  it  is  obvious  that  they 
consist  of  minute  ice  crystals.  Cirri  may  form  above 
another  cloud,  the  two  being  apparently  related,  but  they 
never  form  under  other  clouds. 

Cumulus  clouds  are  the  day  clouds  of  summer  weather. 
They  appear  like  great,  rounded  domes  resting  on  a  liori 
zontal  base.  A  gently  warmed  current  of  air  rises  until, 
being  chilled  both  by  expansion  and  great  altitude,  con- 
densation begins.      The  process  continues  until  a  dense 


THE   MOISTURE   OF   THE   ATMOSPHERE    237 

mass  of  cloud  is  formed.  This  form  is  the  almost  miiver- 
sal  cloud  of  tropical  regious.  It  is  abundant  in  warm 
temperate  climates,  but  rare  in  cold  latitudes.  It  does  not 
form  at  uiglit  nor  in  cold  weather,  for  the  simple  reason 
that  the  up-draught  of  Avarm  air  is  too  feeble,  and  there  is 
not  enough  vapor  present  to  form  clouds  of  sensible  dimen- 
sions. Ordinarily,  cumulus  clouds  have  no  especial  sig- 
nificance as  weather  forecasters.  They  indicate  nothing 
more  than  the  presence  of  moisture,  and,  as  a  rule,  their 
size  shows  whether  there  is  considerable  vapor  or  oidy 
a  little.  If,  however,  a  mass  of  cloud  loses  its  flat  base, 
becoming  ragged  or  festooned  at  the  lower  side,  it  usually 
portends  high  winds  and  local  showers. 

Stratus  clouds  are  so  called  because  they  are  flat  layers 
of  nearly  uniform  thickness.  Normally  the}^  are  the  low- 
est of  all  clouds,  and  probably  contain  the  greatest  amount 
of  foreign  matter.  These 
clouds  are  commonly  ob- 
served at  morning  and  even- 
ing, and  stillness  of  air  is 
essential  to  their  formation. 

The  Nimbus  is  the  shape- 
less rain-cloud  tliat  hovers 
near  the  surface  of  the  earth. 
The  upper  part  consists  of 
light  fog  or  mist ;  the  lower, 

of  falling  drops.  Usually  it  seems  to  form  in  clear  air,  and 
it  gathers  when  the  temperature  reaches  the  dew  point. 

Clouds  are  moved  hither  and  thither  by  the  wind,  but 
the  matter  composing  the  cloud  is  usually  in  motion  even 
when  the  air  is  still.  A  casual  inspection  of  any  summer 
cloud  shows  thiit  it  is  constantly  moving  within  itself. 
Practically,  cloud  is  floating  moisture,  but  in  reality  the 
minute  drops  are  always  slowly  falling.     'I'hc  diophl   falls 


STRATUS   CLOUDS 


238  PHYSICAL   GEOGRAPHY 

imtil  it  reaches  a  region  of  greater  warmth  ;  then  it  is 
changed  to  vapor,  and  the  latter  at  once  ascends  until  it  is 
again  condensed — the  process  being  constantly  repeated. 

Rain. — The  difference  between  rain  and  cloud  consists 
very  largely  in  the  size  of  drops,  but  there  is  also  a  differ- 
ence in  their  physical  condition.  The  drops  of  cloud 
matter,  or  "  water  dust,"  are  minute,  and  practically  they 
float  in  the  air ;  those  of  rain  are  each  many  thousand 
times  as  large,  and  fall  quickly  to  the  ground.  The  causes 
that  operate  to  produce  fog  and  cloud,  however,  also  pro- 
duce rain — namely,  the  cooling  of  water  vapor  below  the 
dew-point. 

The  vapor  precipitated  as  rain  may  pass  through  the 
cloud  stage,  it  is  true  ;  but  the  latter  is  one  of  short  dura- 
tion, and,  as  a  rule,  when  condensation  begins,  it  proceeds 
very  rapidly.  Kain  is  rarely  associated  with  fair-weather 
clouds,  and,  excepting  local  showers,  is  not  derived  from 
them.  In  almost  every  instance  general  rains  are  derived 
from  warm  ocean  winds  that,  blowing  inland,  are  chilled. 

In  general,  more  rain  falls  in  tropical  regions  than 
elsewhere  :  does  the  map  confirm  this  statement  ?  The 
equatorial  cloud-ring  is  also  a  rain-belt,  and  under  it  pre- 
cipitation is  almost  continuous.  The  amount  of  rain  fall- 
ing in  the  torrid  zone  is  sufficient  to  cover  it  to  a  depth 
probably  of  more  than  one  hundred  inches.  In  the  tem- 
perate zone  it  is  a  little  more  than  one-third,  and  in  polar 
regions  about  one-eighth  as  much. 

Rainfall  is  not  uniform  for  all  places  in  the  same  lati- 
tude." On  slopes  that  face  ocean  winds  it  is  greatest, 
while  in  regions  shut  off  from  the  sea  by  high  ranges  it  is 
little  or  nothing.  For  example,  on  the  southern  slope  of 
the  Himalayas  the  precipitation  varies  from  two  hundred 
to  six  hundred  inches ;  on  the  north  side  it  is  less  than 
ten.  On  the  western  slope  of  the  Sierra  Nevada  and  Cascade 


240  PHYSICAL   GEOGRAPHY 

Ranges  it  is  ten  times  as  great  as  on  the  eastern.  Explain 
why  the  dillereuce  exists. 

As  a  rule,  precipitation  is  greatest  at  the  coast  and  de- 
creases toward  the  interior.'^  On  the  Atlantic  coast  of 
the  United  States  it  is  nowhere  less  than  forty  inches ; 
west  of  the  one  hundredth  meridian  it  is  less  than  fifteen. 
On  the  northern  shores  of  South  America  it  is  over  one 
hundred  inches ;  a  few  hundred  miles  inland  it  is  about 
one-quarter  as  much.  In  the  uplands  of  the  eastern  slope 
of  the  Andes  it  again  increases  ;  why  ? 

Not  only  does  the  amount  of  rainfall  vary  in  different 
localities,  for  the  reasons  noted,  but  there  is  also  much 
difference  in  the  time  of  its  distribution.  In  some  local- 
ities it  comes  in  the  form  of  occasional  showers  ;  in  others 
long  periods  of  rain  and  drought  alternate  at  given  inter- 
vals " — that  is,  the  rainfall  is  periodical  and  seasonal. 

An  examination  of  the  wind  chart,  p.  221,  wall  help  to 
explain  this  fact.  The  slopes  of  the  continents  that  face 
ocean  winds,  as  a  rule,  have  periodical  rains.  Thus,  the 
w^estern  coast  of  North  America  faces  the  Prevailing  West- 
erlies of  the  Pacific  Ocean.  In  summer  these  wdnds  are 
blowing  into  a  region  that  is  warmer,  and  therefore  but 
little  rain  falls.  In  winter,  on  the  other  hand,  the  temper- 
ature of  the  land  is  much  lower,  and  therefore  rain  may 
be  of  daily  occurrence. 

On  the  Mexican  coast,  where,  on  account  of  low  latitude, 
the  climate  is  almost  always  mild,  but  little  rain  falls. 
Along  the  coast  of  the  United  States  it  varies  from  ten  or 
twelve  inches  at  San  Diego  to  sixty  or  seventy  at  Puget 
Sound;  while  at  Sitka,  Alaska,  it  is  about  one  hundred 
inches.  How  will  the  difference  in  latitude  explain  this  ? 
In  what  part  of  the  Pacific  Coast  of  South  America  are 
the  conditions  similar?  On  the  Atlantic  coast  of  Europe 
the  conditions  are  much  the  same  ;  most  of  the  precipita- 


THE   MOISTUKE   OF   THE   ATMOSPHERE     211 

tion  occurs  duriug  the  winter  mouths,  but  on  account  of 
high  latitude  a  considerable  rain  falls  in  summer. 

In  tropical  regions,  where  the  winds  have  an  easterly 
origin,  the  easterly  slopes  receive  tlie  heaviest  fall  of  rain. 
In  these  regions,  however,  the  rainfall  follows  the  passage 
of  the  equatorial  cloud-belt  back  and  forth.  This  belt  is 
comparatively  narrow  —  scarcely  five  hundred  miles  in 
breadth.  Duiiug  the  spring  months  of  the  Northern 
Hemisphere  it  moves  northward  Avith  the  sun,  deluging 
the  land  over  w^hich  it  passes  with  almost  continuous  rain. 
After  reaching  its  northern  limit  it  turns  southward,  re- 
passing over  the  same  belt.  In  the  American  continent 
the  cloud-belt  does  not  pass  far  south  of  the  equator  ;  in 
Africa  it  reaches  much  farther  south. 

A  moment's  study  will  show  that  at  each  tropic,  or  limit  of 
the  cloud-belt,  there  will  be  one  rainy  and  one  dry  season, 
w^hile  at  intervening  latitudes  there  may  be  two.  Which 
of  these  conditions  applies  to  Cuba?  to  the  Central  Amer- 
ican states  ?  to  the  Caribbean  coast  of  South  America  ? 

Regions  swept  by  monsoons  usually  have  periodical 
rains  also.  The  reason  is  obvious  :  during  one  part  of  the 
year  the  winds  blow  from  the  land  ;  the  remaining  time 
from  the  sea.  Tlie  rains  of  the  Indian  coast  of  Asia  are 
an  excellent  example.  During  the  winter  months  of  the 
northern  hemisphere  the  prevailing  winds  are  land  winds; 
but  with  the  bursting  of  the;  Ai)ril  monsoon  tlu;  season  of 
heavy  rain  begins  and  the  parched  land  is  (luickly  covered 
with  verdur<'. 

A  large  part  of  the  land  surface  of  the  earth  is  watered, 
not  by  seasonal  and  periodical  i-ains,  but  l)y  the  i)ve- 
cipitation  that  comes  with  the  irregular  inovemeiits  of  tli<' 
atmosphere  known  as  slonnH.  These  regions  as  a  rule  aiv 
either  far  inland,  or  else  high  mountain  ranges  shut  thrni 
off  from  the  reach  of  ocean  winds. 


243  PHYSICAL   GEOGRAPHY 

Tluit  part  of  the  TTnited  States  east  of  tlie  Rocky 
Mountains  is  au  example.  The  ranges  of  the  great  high- 
lands precipitate  practically  all  the  moisture  brought  from 
the  Pacific,  and  therefore  there  are  uo  periodical  rains. 
Moisture  gathers  from  the  Gulf  and  also  from  the  ocean, 
but  for  the  greater  part  it  is  not  precipitated  until  the 
cj'clonic  movement,  which  constitutes  the  storm,  takes 
place.  These  disturbances  occur  so  frequently,  and  there 
are  so  many  of  them,  that  almost  every  part  of  the  region 
receives  a  plentiful  supply  of  moisture.  Similar  con- 
ditions exist  in  parts  of  Eurasia  and  Africa. 

Effects  of  Altitude. — As  a  rule,  more  rain  falls  at  sea- 
level  than  at  higher  altitudes  :  very  little  falls  above  the 
height  of  ten  or  twelve  thousand  feet.  On  mountain- 
slopes,  however,  the  greatest  precipitation  takes  place  be- 
low three  thousand  and  five  thousand  feet.  The  reason  is 
two-fold.  In  moderately  warm  regions  rain  clouds  com- 
monly do  not  reach  much  above  this  altitude  ;  moreover 
at  this  height  the  ground  may  be  cold  enough  to  condense 
moisture  when  it  is  too  warm  to  do  so  at  a  lower  level. 
This  fact  is  often  observed  in  desert  regions. 

Rainless  Regions.— There  are  two  principal  causes 
for  the  existence  of  rainless  regions.  There  may  be  a 
barrier  of  high  mountains  that  shut  off  rain -bearing  winds; 
or,  vapor  may  pass  into  a  warmer  region  where  it  cannot 
be  condensed.  The  Basin  Region  of  the  western  high- 
lands, the  basin  north  of  the  Himalaya  Mountains,  and  the 
Andine  desert,  are  examples  showing  the  effects  of  moun- 
tain barriers.  The  mountains  reach  higher  than  the  rain 
winds.  The  two  African  deserts  and  much  of  the  Mexican 
coast  show  the  effects  of  hot  inland  regions.  The  ocean 
winds  that  penetrate  these  regions  are  warmed  and  not 
cooled,  and  therefore  they  are  relatively  drier. 

Snow. — -When  the  condensing  vapor  freezes  before  it 


THE   MOISTUEE   OF   THE   ATMOSPHERE    243 

cau  gather  iuto  drops,  snow  results.  It  is  evident,  more- 
over, that  snow  cannot  form  unless  the  temperature  is  as 
low  as  0°  (32°  F.).  If  condensation  takes  place  very 
slowly  in  still  air,  the  frozen  droplets  aggregate  into  beau- 
tiful crystalline  forms,'-  but  if  condensation  is  rapid,  each 
flake  is  a  tangle  of  broken  crystals. 

Inasmuch  as  snow  depends  on  a  low  temperature,  it  is 
evident  that  the  distribution  is  governed  both  by  latitude 
and  altitude.  In  polar  regions  snow  covers  the  ground 
the  greater  part  of  the  year,  and  at  a  little  distance  from 
the  sea  it  never  melts.  In  equatorial  regions  the  line  of 
jjerpetual  snow  is  about  sixteen  thousand  feet  above  sea- 
level  ;  in  temperate  latitudes  it  varies  from  seven  thousand 
to  twelve  thousand  feet. 

Hail. — Hail  consists  of  pellets  of  ice,  formed  in  the  air, 
and  a  shower  of  them  constitutes  a  hailstorm.  Usually  a 
hailstorm  consists  of  alternate  shells  of  snow  and  crystal- 
line ice.'^  In  some  instances  sharp,  dog-toothed  cr3'stals 
of  ice  project  from  the  outer  surface.  Hailstones  vary 
in  size  from  tin}'  pellets  to  masses  an  inch  in  diameter. 
Larger  stones  occur,  but  they  are  formed  by  the  cohesion 
of  small  ones.  Hailstorms  are  more  frequent  in  warm 
weather  than  in  cold.  For  reasons  unknown  certain  h)c;d- 
ities  are  especially  subject  to  them.  They  ver^  frequently 
accompany  thunderstorms. 

QUESTIONS  AND  EXERCISES— Find  the  annual  rainfall  of  the 
neighborhood  in  which  you  live  by  striking  an  average  of  the  yearly 
precipitation  for  at  least  ten  years.  (The  statistics  may  be  teamed  fivm 
the  nearest  Weather  Station.) 

Make  a  record  of  the  early  and  late  frosts  for  the  year  What  fruit 
crops  are  injured  by  killing  frosts  in  the  neighborhood  in  which  you 
live  ? 

Learn,  from  the  nearest  Weather  Station,  the  months  in  which  the 
greatest  amount  of  rain  or  snow  falls  ;  —the  least 

What  crops  or  plants  of  commercial  value  would  suffer  or  perish 


244  PHYSICAL   GEOGRAPHY 

if  the  rainfall  in  the  State  in  which  you  live  were  decreased  one- 
third  ? 

Note  the  character  and  kinds  of  cloud  visible  during  several  days ; 
at  what  time  were  stratus  clouds  visible  ? 

Explain  how  smoke  may  gradually  gather  cloud  matter.  Why  is 
this  most  apt  to  take  place  toward  evening  ? 

The  receiver  of  a  rain  gauge  is  a  cylindrical  cup  four  inches  in  diame- 
ter. For  convenience  of  measurement  the  water  caught  is  poured  into 
a  glass  tube  one  inch  in  diameter  :  a  depth  of  one  inch  of  rain  in  the 
receiver  will  make  how  many  inches  in  the  tube  ? 

Explain  how  a  crust  forms  on  the  surface  of  snow. 

At  a  convenient  opportunity,  catch  flakes  of  snow  on  a  piece  of  black 
cloth ;  examine  them  with  a  magnifying-glass  and  make  drawings  of 
their  shapes.     (  Obsewe  the  conditions  noted  on  p.  243.) 

COLLATERAL   READING   AND   REFERENCE 

Tyndall. — Forms  of  Water. 

U.  S.  Weather  Bureau. — Monthly  Weather  Review.  Mid- 
summer and  midwinter  issues  of  any  year. 

Greely. — American  AVeather— pp.  77-81,  134-162. 
Waldo. — Elementary  Meteorology— pp.  142-165. 


NOTES 

'  The  expressions  "air  absorbs  water  in  the  form  of  a  vapor  " 
and  "  warm  air  can  hold  more  water  vapor  than  cold  air  "  are  so 
popular  that  ordinarily  they  pass  for  scientific  truths.  They  are 
certainly  convenient,  but  a  moment's  reflection  shows  them  to 
be  inexact. 

^The  phenomenon  popularly  known  as  "the  sun  drawing 
water  "  is  due  to  the  passage  of  rays  of  light  through  rifts  in  the 
clouds.  The  passage  of  the  rays  is  marked  by  minute  dust-moats, 
which  reflect  and  scatter  some  of  the  light. 

'  At  times  it  may  be  noticed  that  wet  clothing  exposed  all  day 
to  the  air  refuses  to  dry.  The  reason  is  that  the  air  is  already 
saturated,  and  because  of  this  no  further  evaporation  can  take 
place. 

Sometimes  dew  forms  copiously  with  but  a  slight  fall  of  tem- 
perature, while  perhaps  on  a  following  night,  none  may  appear, 


THE    MOISTURE    OF   THE   ATMOSPHERE     245 


though  the  temperature  is  much  lower.  An  inspection  of  the 
table  on  p.  380,  will  explain  how  this  may  occur.  If  there  were 
seven  grains  of  water  vapor  in  each  cubic  foot  of  air,  a  fall  of 
temperature  from  68°  (F.)  to  64°  would  be  attended  with  dew  ; 
but  if  only  three  grains  were  present,  the  thermometer  might 
sink  as  low  as  40°  without  any  sign  of  dew. 

^A  cloth  screen  within  four  or  five  feet  of  the  ground  will  have 
the  same  effect. 

'These  cloud  banners  were  noticed  in  the  Alps  bj*  Professor 
Tyndall,  and  were  first  described  by  him.     They  may  be  often 
seen  streaming  from  the  summit  of  Tacoma,  Washington,  and 
the    alleged    smoke    from   the 
crater  of  Mount  Hood,  Oregon, 
is  nothing   but  a  similar  phe- 
nomenon. 

'  This  indication  has  had  a 
recognized  place  in  weather- 
lore  for  two  thousand  years. 
It  is  mentioned  in  Virgil  : 

Tenuia     .     .     lanae  per  ccelutn  val- 

lera  fern,  .MACKEREL  SKY 

and  it  is  found  among  Teutonic  peoples,  as  well  ;  hence  the 
popular  saying — 

Mackerel  sky,  twelve  hours  dry. 

*Not  infrequently  a  column  of  smoke,  from  a  factory  chimney 
or  a  steamer's  smoke-stack,  becomes  the  nucleus  of  a  stratus 
cloud.  The  smoke  ascends  until  buoyancy  and  gravity  balance 
each  other,  and  then  settles  in  the  form  of  a  thin,  flat  layer. 
Each  particle  becomes  a  surface  of  condensation,  and  the  cloud 
matter  continues  to  gather  until  it  is  swept  away  by  the  wind, 
or  the  conditions  are  changed. 

'The  heaviest  annual  fall  is  probably  at  Cherrapun.ii.  India, 
where  the  average  is  about  500  inches.  In  August,  1841,  the  total 
fall  for  the  month  was  264  inches,  and  in  1861  the  yearly  fall 
reached  the  enormous  amount  of  1)05  inches — about  2.5  inclies  a 
day  !  On  June  14,  1876,  40.6  inches  fell  in  twenty-four  hours. 
In  the  three  days  ending    February,    ISit:;,  an  aggn-gatc  of  :{5.8 


24G  I'llYSiCAL   GEOGRAPHY 

iiii'hcs  fell  at  Brisbane,  Australia.  In  the  United  States  21.4 
iiu'hes  I'ell  at  Alexandria,  Louisiana,  in  one  day,  and  at  Triadel- 
pliia,  West  Virginia,  0.9  inches  fell  in  fifty-five  minutes.  All 
these  instanees,  however,  are  very  unusual.  Commonly,  not 
more  than  two  inches  fall  in  a  day. 

'"  The  greater  the  distance  from  the  coast  the  more  abnormal 
is  the  character  of  the  rainfall.  In  the  Basin  Region  of  the  west- 
ern United  States,  the  rain  is  restricted  to  showers  of  short  du- 
ration, and  these  often  take  the  form  of  cloud-hursts.  There  is  a 
sudden  darkening  of  the  sky,  a  terrific  downpour  of  water — 
perhaps  thi-ee  or  four  inches  in  fifteen  minutes— and  then  the  sun 
is  again  licking  up  the  water  from  the  almost  hissing  rock  waste. 
The  specific  cause  of  cloud-bursts  is  not  known. 

"  In  regions  visited  by  periodical  rains,  not  infrequently  the 
air  is  so  loaded  with  dust,  at  the  end  of  the  dry  season,  that  the 
first  rain  is  discolored  and  even  muddy.  The  yellow  and  golden 
rain,  once  a  great  mystery,  is  commonly  due  to  the  pollen  of 
pine.  Examined  under  a  microscope  the  character  of  this  pollen 
is  such  as  to  leave  no  doubt  as  to  its  origin.  Showers  of  frogs, 
fishes,  and  angleworms  (!)  have  been  reported,  but  not  an  in- 
stance has  been  substantiated.  It  is  not  impossible  that  a  water- 
spout might  whirl  a  school  of  fishes  into  the  air,  and  then  over 
the  land,  but  no  tornado  known  has  been  so  selective  as  to  con- 
fine itself  exclusively  to  frogs  and  angleworms.  The  latter  sim- 
ply emerge  from  their  hiding-places  at  the  onset  of  the  shower. 
Among  other  abnormal  showers  are  the  rains  from  cloudless  skies. 
Instances  are  common,  especially  in  mountainous  localities.  The 
precipitation  in  such  cases  is  very  slight  and  the  showers  rarely 
cover  more  than  a  square  mile  or  two.  The  sky  is  cloudless 
merely  because  there  are  not  enough  drops  in  the  air  at  any 
moment  noticeably  to  interrupt  the  light. 

'-  With  one  or  two  exceptions  all  the  illustrations  of  snow 
crystals  are  copies  of  drawings  made  in  the  arctic  regions  by 
Captain  Scoresby.  A  few  drawings  have  been  made  by  Professoi 
Tyndall,  and  recently  excellent  photographs  have  been  obtained  ; 
these  show  that  ice-crystals  and  snow-flakes  are  not  so  regular 
nor  so  complicated  in  structure  as  those  observed  by  Scoresby. 
In  order  to  obtain  good  specimens  of  crystals,  they  must  be 
gathered  on  a  perfectly  still  day  when  the  temperature  is  several 
degrees  below  the  freezing-point.     It  is  best  to  catch  them   on  a 


THE   MOISTURE    OF   THE   ATMOSPHERE     247 

piece  of  black  cloth,  and  if  they  are  to  be  examined  under  a  mi- 
croscope the  glass  slide  on  which  the  flake  rests  should  be  covered 
with  the  same  material.  The  crystalline  forms  observed  in  sun- 
shine are  materially  different  fi'om  those  found  in  cloudy  weather. 
'^  The  peculiar  structure  of  hail-pellets  has  led  to  the  theory 
that  the  stone  has  been  whirled  alternately  into  warm  and  cold 
layers  of  air;  this  is  only  a  supposition,  and  concerning  their 
formation  nothing  certain  is  known.  As  a  theory,  however,  it  is 
not  unreasonable.  Ordinarily,  hail-storms  are  of  only  a  few 
minutes'  duration,  and  the  amount  falling  is  a  small  fraction  of 
an  inch  in  depth.  In  1888,  at  Moradabad,  India,  hail  fell  to  a 
depth  of  several  inches,  and  in  one  district  two  hundred  and 
thirty-five  people  were  killed.  In  June,  1879,  a  storm  swept  over 
central  New  York  and  Massachusetts,  during  which  stones  seven 
inches  in  circumference  fell.  In  July,  1880,  a  hail-storm  destroyed 
the  crops  in  the  vicinity  of  Waupaca,  Wisconsin.  The  shower 
covered  an  area  of  forty  square  miles.  Stones  from  six  to  ten 
inches  in  circumference  fell.  In  July,  1881,  the  fall  of  hail  at 
Cumberland,  Maine,  was  so  great  that  drifts  two  feet  deep  were 
observed  twelve  hours  afterward.  In  June,  1882,  at  Dubuque, 
Iowa,  stones  weighing  twenty-eight  ounces  were  found.  In 
August,  1883,  at  Gray,  Iowa,  the  drifting  hail  covered  the  fence 
tops.  In  June,  1886,  so  much  hail  fell  in  Grand  Forks  County, 
Dakota,  that  it  did  not  all  melt  for  thirty  hours.  In  a  single 
storm  that  passed  over  a  small  area  in  Dakota,  a  quarter  of  a 
million  acres  of  wheat  were  destroyed. 


CHAPTEK  XIV. 


THE     MOISTURE     OF 


THE    ATMOSPHERE. 
STORMS 


CYCLONIC 


Both  ou  the  land  and  at  sea  there  are  regions  of  con- 
siderable area  that  normally  are  not  swept  by  regular  and 
constant  winds.  On  the  sea  these  are  the  calm  belts ;  on 
the  land  they  are  regions  from  which  the  winds  are  shut 
off  by  mountain-ranges  or  disturbed  by  broad  stretches 
of  land.  On  the  sea  the  shifting  of  the  calm  belts  wdtli  the 
season  brings  various  parts  successively  under  the  influ- 
ence of  the  regular  winds. 
On  land  the  regular  Avinds 
usually  exist  as  upper  cur- 
rents, while  at  the  surface 
the  wdnds  are  local  and  vari- 
able ;  the  upper  currents, 
moreover,  are  so  high  that 
they  are  too  cold  to  contain 
much  moisture. 

Such  regions  do  not  re- 
ceive seasonal  rains.  The 
land  areas,  in  some  instances,  receive  none  at  all,  except  from 
an  occasional  cloud-burst ;  but  in  many  cases  a  consider- 
able rainfall  results  from  the  movements  of  local  winds. 
That  part  of  the  United  States  east  of  the  Rocky  Moun- 
tains is  an  excellent  illustration.  It  receives  no  moisture 
directly  from  the  constant  winds  ;  yet  about  every  part  of 
it  east  of  the  2,000-foot  contour  is  so  generously  supplied 

248 


STRATUS   CLOUDS   DISTURBED   BY 
AN   UP-DRAUGHT 


CYCLONIC   STORMS 


249 


with  rain  that  it  is  oue  of  the  most  productive  regions 
of  the  workl. 

Whenever  a  local  wdnd  occiu's,  one  of  two  conditions  is 
pretty  apt  to  exist.  Either  there  is  an  up-draught  toward 
which  the  wind  is  blowing,  or  else  there  is  a  great  accumu- 
lation of  air  from  which  the  air  is  spreading  outward. 
These  local  disturbances 


50 

N.     HEMISPHERE 

50 

-iC^^ 

40 

r^y^ 

40 

30 

20 

{iT~'^^^'^ 

30 
20 

^^>v. 

^vl^IVw 

10 

Cic-.-. 

10 

10 

EQUATORIAL       C4LMS 

0 

10 

W^$^" 

20 

r^P^^ 

20 

30 

^Onv-Z' 

30 

40 

\^y~^ 

40 

50 

^-"v^^ 

50 

S.     HEMISPHERE 

constitute  the  condi- 
tions jDopularly  known 
as  storms.  Moreover,  in 
either  case  the  move- 
ment of  the  air  sooner 
or  later  develops  into  a 
whirl.  The  wind  that 
blows  toward  an  up- 
draught  or  a  depression 
forms  a  cyclone ;  that 
which  blows  outward 
from  a  high  bank  of  air, 
an  anticyclone.  These 
disturbances  originate 
both  on  the  land  and  at 
sea.  The}-  are  usually 
indicated  by  a  changing 
barometer  ;  hence  a  cy- 
clone is  often  described  as  an  area  of  low  barometer — or 
simply  a  "Low" — and  the  anticyclone,  one  of  high  bu 
r(jmeter.  As  a  rule  both  the  cyclone  and  the  anticyclone 
are  local  disturbances,  and  therefore  they  are  carried  along 
by  the  great  currents  of  the  air,  just  as  an  eddy  formed  in 
a  river  is  carried  along  in  its  flood. 

Cyclonic  movements  therefore  travel  westwardly  in  low- 
latitudes  and  eastwardly  in  latitudes  beyond  tlio  trojiics, 
because  these  are  the  prevailing  directions  ol'  tlic  winds. 


NORMAL  CYCLONE  TRACKS 


350 


PTT  YSTC  A  L   GEOG  K  A  PHY 


l^ocanse  of  this  fact,  when  a  cyclone  has  once  formed,  the 
track  alono-  which  it  is  likel}-  to  move  can  be  predicted 
with  considerable  accuracy.^  The  direction  of  the  whirl 
has  been  learned  by  experience  :  in  the  Northern  Hemi- 
sphere it  is  opposite  that  of  the  clock's  hands  ;  in  the 
Southern  Hemisphere,  the  reverse.-'  A  knowledge  of 
these  facts  enables  the  mariner  to  avoid  a  cyclone,  and 
also  to  steer  ont  of  it  when  overtaken  by  one. 

Tropical  Cyclones.— Tropical  cyclones  usually  origi- 
nate within  a  few  degrees  of  the  equator.  They  are  the 
hurricanes  of  the  West  Indies  and  the  fjfphoons  of  the 
Cliina  Sea.  The  storm  area  extends  over  a  surface  vary- 
ing from  a  few  hundred  to 
more  than  a  thousand  miles 
in  diameter.  The  preced- 
ing illustration,  p.  249,  shows 
roughly  the  track  which,  or- 
dinarily, one  of  them  fol- 
lows. What  is  its  direction 
in  tropical  latitudes  ?  in  lati- 
tudes beyond  the  tropics? 
Note  the  direction  of  the 
wlnrl  in  each  hemisphere. 
It  rarely  extends  beyond  the  60th  parallel. 

The  real  beginning  of  the  tropical  cyclone  is  the  dead 
calm  that  for  a  few  days  precedes  the  disturbance,  for 
it  is  only  when  the  air  is  in  a  state  of  rest  that  the 
necessary  conditions  can  obtain.^  The  first  essential  con- 
dition is  the  overheating  of  the  air  next  the  sea — pre- 
cisel}^  the  same  condition  that  formed  the  beginning  of 
the  desert  whirl  (p.  224).  But  while  the  stratum  of  air 
that  causes  the  desert  whirl  is  only  a  few  hundred  feet 
in  height  and  involves  a  very  small  area,  the  atmo- 
sphere  disturbed    by   the   tropical   cyclone   is,    perhaps, 


"STREAMERS"   OF   CIRRUS   CLOUDS 
—  THE   FORECAST   OF   A   CYCLONE 


CYCLONIC   STORMS  251 

several  thousand  feet  high  and  man}'  thonsaud  miles  in 
extent. 

The  longer  the  sun  beats  down  on  the  glassy  sui-face  of 
the  water  the  greater  will  be  the  energy  of  the  storm  when 
it  begins.  Moreover,  there  is  one  element  present  in  the 
tropical  cyclone  that  is  not  foimd  in  the  case  of  the  desert 
whirl — namely,  tlie  vapor  of  water — and  this  is  the  most 
important  distinction  between  the  two.  Finally  the  equili- 
brium becomes  so  imstable  that  a  slight  up-draught  of  air 
occurs  where  the  resistance  is  least.  The  moment  this 
occurs,  the  rising  air  already  near  the  dew-point  is  chilled 
by  its  own  expansion,  and  a  part  of  its  moisture  is  precip- 
itated. The  fall  of  rain  sets  free  an  enormous  amount  of 
latent  heat,  and  a  furious  up-draught  at  once  takes  place. 

It  is  the  latent  heat  of  the  moisture  set  free  that  gives 
to  the  cyclone  its  great  energy.  This  indeed  is  its  fuel, 
and  so  long  as  the  supply  lasts,  just  so  long  will  the  cy- 
clone continue.  The  ascending  air  at  first  is  very  moist 
and  tolerably  warm.  But  after  its  moisture  has  been  con- 
densed the  latent  heat  set  free  renders  it  dry  and  very 
much  warmer,  thereby  increasing  the  up-draught. 

The  nearer  the  centre  of  the  cyclone,  the  stronger  is  the 
wind.  The  "eye"  of  the  storm,  or  the  centre  of  the 
whirl,  is  the  uj^-draught  of  the  cyclone,  and  here  brief  in- 
tervals of  sunshine  alternate  with  torrents  of  rain.  In  the 
centre  of  the  storm  the  barometer  stands  lowest — perhaps 
two  inches  h:>wer  than  it  is  beyond  the  edge  of  the  storm. 

The  path  of  the  cyclone  seems  at  first  to  be  one  of  un- 
usual shape,  but  when  examined  in  relation  to  tlx^  luvvnil- 
ing  winds  the  mystery  disappears.  It  is  not  nnlikily  tli;it 
the  temperature  of  the  upper  air  has  much  to  di>  with  tin; 
northerly  tendency  of  the  cyclone;.  Because  cold  air  is  rel- 
atively heavier  than  light  air,  the  coldcjr  the  upprr  air 
that  surrounds  the  up-draught,  the  more  vigorous  will  the 


352  rilYSlOAL   GEOGEAPHY 

latter  be.  In  the  Northern  Hemisphere  the  cohler  air  lies 
to  the  northward  of  the  storm,  and  this  will  be  the  direc- 
tion of  least  resistance. 

Knowing  the  direction  of  the  whirl  and  the  path  of  the 
storm,  it  is  not  dithcult  to  lay  the  course  of  tho  vessel  out 
of  the  way  of  the  cyclone.  For  this  purpose  "  storm- 
cards,"  or  diagrams  similar  to  that  on  p.  263,  are  conven- 
ient. The  distance  of  the  storm-centre  can  be  estimated 
only  to  a  rough  degree,  but  the  bearings  can  be  obtained 
with  a  high  degree  of  probability.  Facing  the  wind  the 
storm-centre  is  on  the  right  hand.'' 

Winter  Cyclones. — Some  of  the  fiercest  storms  of  the 
higher  latitudes,  however,  do  not  originate  anywhere  within 
tropical  regions.  These  are  the  extra-tropical  or  winter 
cyclones,  and  the  fierce  winter  storms  of  the  North  Atlan- 
tic Ocean  are  examples.  It  is  evident  that  these  storms 
cannot  originate  in  a  dead  calm,  because  there  is  no  long- 
continued  calm  weather  where  they  form  ;  and  it  is  equally 
apparent  that  they  are  not  formed  by  the  overheating  of 
the  air  next  the  surface  of  the  water. 

It  is  thought  that  these  storms  result  from  the  intrusion 
of  cold,  noi'th  winds  into  the  region  of  warm  and  moist 
air,  to  the  southward.  In  any  case  the  condensation  of 
moisture  creates  an  up-draught  that  quickly  develops  into 
a  whirl.  But  if,  at  the  time  of  intrusion,  the  cold  air  takes 
the  upper  position,  the  equilibrium  becomes  much  more 
unstable,  and  the  storm  very  likely  develops  into  one  of 
great  fury.^ 

Land  Storms. — The  occasional  local  squalls  excepted, 
all  the  storms  of  the  land  are  cyclonic  in  nature,  and 
except  in  violence  they  do  not  differ  materially  from  the 
cyclones  of  the  sea.  In  nearly  every  case  they  follow  the 
same  courses  that  are  taken  by  the  latter — westerly  in 
tropical  and  easterly  in  temperate  latitudes. 


CYCLONIC   STOEMS 


253 


Since  the  establishment  of  the  various  weather  bureaus, 
the  storm-tracks  have  been  closely  studied,  and  it  is  found 
that  most  storms  follow  certain  lines  or  belts. 

In  the  United  Stiites  two  storm-tracks  are  apparent.® 
The  lesser  number  follow  the  trend  of  the  Atlantic  coast. 
The  storms  usually  overlap  the  shore  and  the  coast  plain, 
but  they  seldom  extend  west  of  the  Appalachian  highlands. 
These  storms 
belong  to  the 
class  of  West 
Indian  cyclones. 
They  originate 
in  the  Caribbean 
Sea,  and  turning 
n  o  r  t  h  w  a  r  d , 
finally  reach  the 
latitude  of  the 
Middle  Atlantic 
coast. 

Most  of  the 
storms  that  pre- 
vail in  the  Unit- 
ed States  form 
near  the  great 
highlands  of  the 
west — very  fre- 
quently near  the 

eastern  base  of  the  Kocky  Mountains,  crossing  the  con- 
tinent in  a  northeasterly  direction.  These  storm -tracks 
have  a  distinct  tendency  to  shift  north  or  south  with  tlio 
apparent  motion  of  the  sun,  the  belt  being  a  little  farther 
north  in  summer  than  in  wiiitin-.  The  valley  of  tlie  St. 
Lawrence  Itiver  and  the  basin  of  the  Great  Lakes  is  a 
common  track. 


A  STORM,  OR  AREA  OF  LOW  BARUWh  ll.K 

The  shaded  part  is  the  area  of  rain  ;  the  dotted  region  the  area 
of  cloudiness.     The  arrows  fly  with  the  wind. 


254  PHYSICAL   GEOGRAPHY 

Altliougli  they  are  sometimes  accompanied  by  local 
squalls,  laud  storms  rarely  exhibit  the  fmy  of  ocean 
cyclones.  The  area  of  the  storm  is  usually  larger,  but 
the  wind  seldom  attains  a  velocity  greater  than  forty 
miles  an  hour.  The  storm-centre  is  distinct,  but  the 
barometer  ma}^  not  fall  more  than  half  an  inch. 

Clouds,  and  rain  or  snow,  accompany  the  majority  of 
storms,  but  the  area  of  rain  does  not  always  cover  the 
whole  extent  of  the  storm  ;  as  a  rule,  most  of  the  cloud 
area,  and  the  rain  as  well,  occur  in  front  of  the  storm- 
centre.  With  the  passage  of  the  latter  there  are  occasional 
hard  showers  in  which  the  rain  falls  almost  verticalh',  or 

perhaps  drives  slightly  tow- 
ard the  east.  These  are  the 
"  clearing  showers." 

Because  the  wind  blows 
toward  the  storm-centre,  it 
IS  evident  that  storms  of  the 
second  class  will  be  pre- 
ceded by  easterly  and  will 
clear  with  westerly  winds. 
Those  from  the  West  Indies 
will  begin  with  northeasterly  and  clear  with  southwesterly 
winds — the  "nor'easters  "  and  "  sou' westers." 

In  some  instances  general  storms  are  accompanied  by 
disturbances  of  a  very  violent  character.  Of  these  the 
most  important  are  thunder-showers,  cold  waves,  and 
tornadoes  and  waterspouts.  Thunder-storms  and  torna- 
does are  local  in  character,  and  often  occur  independently 
of  general  storms.  Waterspouts  and  tornadoes  are  local, 
the  former  being  confined  to  the  water.  Cold  waves  are 
general. 

Cold  Waves.— Just  as  the  trough  of  a  wave  of  the  sea  is 
followed  by  the   crest  of  another  wave,  so  in  the  aerial 


CLEARING   WEATHER   CLOUDS 


CYCLONIC   STORMS  255 

ocean  an  area  of  low  barometer  is  followed  hj  one  of  high 
barometer,  and  if  the  latter  be  an  anticyclone  of  cold  air  the 
result  is  a  cokl  wave. 

Not  infrequently  it  happens  that  the  barometer  is  con- 
siderably higher  on  one  side  of  a  storm-track  than  on  the 
other.  In  such  a  case,  it  is  evident  that  most  of  the  air 
flowing  in  to  fill  the  depression  will  come  from  that  side 
on  which  the  barometer  is  the  higher.  If  the  air  is  drawn 
in  from  the  south  side,  it  is  pretty  apt  to  be  a  mass  of 
warm,  moist  aii',  and  the  farther  north  the  storm  track,  the 
higher  in  latitude  Avill  the  body  of  warm  air  intrude.'  On 
the  contrary,  if  the  bank  of  cold  air  lies  to  the  northward, 
the  depression  will  fill  chiefly  with  cold  air  from  this 
direction. 

In  summer  neither  the  cool  air  nor  the  warm  air,  follow- 
ing the  passage  of  a  storm,  varies  much  more  than  eight  or 
ten  degrees  from  the  usual  temperature.  In  winter,  how- 
ever, if  the  storin-track  lies  well  to  the  south  a  large 
volume  of  very  cold  air  will  be  drawn  far  to  the  south  aud 
the  temperature  may  fall  forty  or  fifty  degrees  in  a  day's 
time,  or  even  in  a  few  hours.**  Ordinarily,  the  cold  wave 
flows  in  not  more  forcibly  than  a  brisk  wind,  but  occa- 
sionally it  advances  with  the  force  of  a  hurricane,  lower- 
ing the  temperature  to  thirty  degrees  or  more  below  zero 
(F.).  In  such  cases  the  cold  wave  is  called  a  blizzard'^  and 
it  is  marked  by  a  furious  downfall  of  snow. 

Tornadoes. — Tornadoes  are  whirling  storms  of  the 
land.  Though  they  cover  a  smaller  area  than  any  other 
storm,  they  are  proba])ly  the  most  violent  atmospheric 
disturbances  known.'"  The  path  of  the  tornado  seldom  ex- 
ceeds thirty  or  forty  miles  in  length,  while  the  destructive 
part  of  the  whirl  is  not  more  than  a  few  rods  in  width. 
Like  other  cyclonic  disturbances,  the  tornado  is  formed  in 
an  area  of  low  barometer.     Seen  at  a  distance  of  one;  or 


256 


PHYSICAL   GEOGRAPHY 


two  miles,  the  tornado  appears  as  a  dense,  black,  funnel- 
sliuped  cloud  hanging  from  rapidly  whirling  clouds  above. 
The  funnel  is  the  centre  of  the  storm,  and  so  rapid  is 
the  whirl  that  it  forms  almost  a  vacuum.  The  rotatory  ve- 
locity of  the  wind  is  thought  to  be  not  far  from  two  miles 
a  minute. 

Between  the  terrific  wind  and  the  vacuous  centre  noth- 
ing can  withstand  the  force  of  the  tornado.  The  stout- 
est  tree-trunks  are  twisted  as  though  they  were   ropes, 

and  in  many  instances 
pulled  clear  out  of  the 
ground.  Buildings  in 
the  way  of  the  funnel- 
cloud  burst  into  pieces 
outwardly  the  moment 
the  latter  envelops  them ; 
heavy  locomotives  are 
lifted  from  the  railway 
track  ;  and  iron  bridges 
are  blown  from  their 
foundations,  twisted  into 
shapeless  tangles,  and 
carried  long  distances. 
Another  noticeable  feat- 
ure is  the  lane  or  "  wind- 
road  "  made  when  a  tor- 
nado passes  through  a 
forest. 

A  close  study  of  sev- 

measure    has    shown   the 

At   the  beginning   of 


A  TORNADO  TRACK. 

The  position  and  direction  of  the  rails  show  the 
direction  of  the  whirl. 


eral    hundred    tornadoes   in    a 

manner  in  which  they  originate 

a  storm  it  sometimes  happens  that  a  great  volume  of  cold, 

dry  air  lies  on  one  side  of  the  disturbance,  while  a  mass 

of  warm,  moist  air  lies  on  the  other  side.     Such  a  con- 


CYCLONIC   STORMS  257 

clition,  iudeecl,  is  not  infrequently  the  immediate  cause  of 
the  storm. 

During  the  progress  of  the  latter  large  volumes  of  cold 
air  are  whirled  into  regions  of  warm  and  moist  air.  Now, 
if  the  heavier  cold  air  lies  next  the  earth,  no  distm-bauce 
follows.  But  if  it  comes  to  rest  on  the  top  of  a  thick  layer 
of  warm  air  the  case  is  different.    The  conditions  are  those 


A  TORNADO  AND  ITS  FUNNEL  CLOUD. 

of  unstable  equilibrium,  and  the  latter  will  sooner  or  later 
be  upset.  There  results  an  up-draught  of  warm  air,  and 
soon  the  whirl  is  in  full  vigor. 

In  about  ninety-five  per  cent,  of  all  the  tornadoes 
studied  the  whirl  accords  with  that  of  other  storms  in  the 
Northern  Hemisphere.  Almost  always  tliey  move  from  the 
southwest  to  tlie  northeast."  In  nearly  every  instance 
thus  far  recorded  the  tornado  track  lies  south  of  a  general 
storm. 


258 


PHYSICAL   GEOGRAPHY 


All  parts  of  the  United  States  are  subject  to  tornadoes, 
but  they  are  most  prevalent  in  the  central  part  of  the  Missis- 
sippi Valley.  West  of  the  102d  meridian  they  are  extremely 
rare,  because  there  is  so  little  moisture  in  the  atmosphere. 
There  is  also  a  belt  south  of  the  Ohio  Ptiver,  in  which 

they  are  infrequent.  They 
rarely  occur  in  mountainous 
regions. 

Tornadoes  are  more  frequent 
in  summer  than  winter.  The 
greatest  number  occur  in  May 
and  more  oc- 
cur in  May, 
June,  and 
July  than  dur- 
ing all  the 
remaining 
months.  They 
are  more  fre- 
quent in  the 
afternoon 
than  in  the 
morning,  and 
rarely  occur 
at  night. 
Waterspouts. — A  waterspout  is  a  whirlwind  of  the  sea 
or  other  large  body  of  water.  The  whirl  is  so  rapid  that 
the  water  is  carried  upward  to  fill  the  vacuous  centre.  The 
lower  part  of  the  waterspout  is  probably  a  nearly  solid 
column  of  water ;  the  upper  part  is  a  rapidly  whirling 
mass  of  spray.  Waterspouts  are  most  common  in  the 
region  of  cyclone  tracks — especially  along  the  track  of  the 
Gulf  Stream.  It  is  usually  asserted  that  the  water  that 
composes  them  is  fresh.      This  is   not  always  the   case, 


EFFECTS  OF  A  TORNADO. 


CYCLONIC   STORMS  259 

however;  in  many  instances  it  is  salt — sea-water,  pure  and 
simple.  In  the  lower  part  the  column  is  not  more  than 
ten  or  fifteen  feet  in  diameter ;  in  the  upper  part  it  is 
whirled  into  a  balloon-shaped  cloud  of  spray  and  mist 
several  hundred  feet  in  width. 

The  white  squall  is  similar  in  origin  to  the  whirl  that  re- 
sults in  a  waterspout ;  in  fact,  it  may  properly  be  called  a 
fair-weather  whirlwind  of  the  sea.  It  is  sufficiently  violent 
to  whirl  a  considerable  volume  of  sea-water  into  spra}', 
but  hardly  strong  enough  to  form  a  waterspout. 

Weather  Forecasting. — Knowing  the  laws  of  storms 
and  normal  atmospheric  movements,  it  is  not  a  difficult 
matter  to  predict  weather  conditions  with  considerable 
accuracy.  In  the  temperate  zones  weather  conditions 
originate  to  the  westward  or  southwestward  of  the  ob- 
server ;  in  tropical  regions,  they  progress  from  the  east- 
ward. 

Except  in  the  extreme  southern  part,  where  disturbances 
are  occasionally  tropical  in  their  movements,  the  weather  of 
the  United  States  is  essentially  of  the  westerly  type.  That 
is,  all  disturbances  progress  from  the  west  or  southwest 
to  the  east  or  northeast. 

The  United  States  AVeather  Bureau'-  was  organized 
for  the  purpose  of  protecting  agriculture,  navigation, 
and  commerce  by  furnishing  information  of  coming  storms, 
dangerous  coast-winds,  threatening  floods,  cold  waves,  and 
killing  frosts.  Scattered  over  the  whole  territory  in 
selected  locations  are  upwards  of  six  hundred  observers 
who,  twice  a  day,  at  the  same  actual  time,  observe  tem- 
peratiu-e,  barometric  pressure,  relative  humidity,  direc- 
tion of  wind,  amount  of  rain  or  snow,  etc.  These  re- 
sults are  telegraphed  to  Washington  and  ciitcivd  ii|».»ii  u 
weather  map. 

Lines  are  drawn  thiough  localities  of  equal   liaroiiietric 


STORM  CENTER  :  FIRST  DAY 


STORM  CENTER: SECOND  DAY 


CYCLONIC   STORMS  261 

pressure,  aud  also  through  h^calities  having  the  same  tem- 
perature. The  former  are  isobars,  the  hitter  isotln'niis. 
lu  this  manner  areas  of  high,  normal,  aud  low  barometer 
are  readily  mapped  and  located.  When  the  direction  of 
the  wind  is  plotted  it  will  be  found  that  it  is  everywhere 
blowing  toward  the  area  of  low  barometer. 

Twelve  hours  afterward,  when  a  new  set  of  observations 
is  plotted,  it  will  be  found  that  the  area  of  low  barometer 
has  advanced  eastward  with  about  the  velocity  of  an  or- 
dinary express  train.  With  this  information  both  the 
direction  and  the  velocity  of  the  storm  cau  be  quite  ac- 
cui'ately  forecast  for  the  succeeding  twenty-foui-  hours. 
Practically  all  general  storms  begin  with  easterly-  and  clear 
with  westerl}'  winds. 

About  ninety  per  cent,  of  the  predictions  may  be  veritied 
and  the  number  actually  veritied  is  very  close  to  the  possi- 
ble limit.  Failure  of  verification  is  due  to  several  causes — 
the  sudden  swerving  of  a  storm  from  its  track,  the  dissipa- 
tion of  a  storm  once  formed,  and  the  unforeseen  develop- 
ment of  a  local  storm.  The  shifting  of  a  storm  one  hun- 
dred miles  on  either  side  of  its  predicted  track  may  nullify 
the  forecasts  over  a  very  large  area. 


QUESTIONS  AND  EXERCISES.— Why  does  the  wind  blow  toward 
a  low  and  away  from  a  high  barometer  ? 

Why  do  cyclonic  movements  of  the  wind  move  toward  the  west  in 
tropical,  and  toward  the  east  in  temperate  latitudes  ? 

Why  does  the  water  flowing  out  of  a  sink  through  a  discharge-pipe 
at  the  bottom  form  a  whirlpool  ? 

In  the  map  at  the  top  of  p.  260,  near  what  city  is  the  centre  of  the 
storm  ?  What  is  the  direction  of  the  wind  at  New  Orleans  and  Baton 
Rouge?— at  St.  Louis  and  Cairo  ?-  at  Chicago  and  Davenport?  at 
Duluth?  — at  Cheyenne?— in  the  greater  part  of  North  and  South 
Dakota  ? 

Name  one  or  two  places  at  or  near  which  the  barometer  is  29.5  inches; 
29.7  inches  ;  29.9  inches ;  30  inches. 


263  PHYSICAL   GEOGRAPHY 

About  how  far  has  the  storm  advanced  at  the  time  of  observation  on 
the  second  day  ? 

Note  the  direction  of  the  wind  at  Pittsburgh,  Cleveland,  Wilming- 
ton, N.  C,  Cincinnati,  Indianapolis,  Chicago,  Springfield,  111.,  Mil- 
waukee, New  Orleans,  Mobile  and  Little  Rock. 

The  wind  whirls  warm,  moist  air  from  the  south  to  colder,  northerly 
latitudes  ;  what  will  be  the  effect  on  the  moisture  ?— on  the  temperature 
of  the  region  over  which  the  storm  passes  ? 

In  what  position,  with  reference  to  the  storm  centre,  is  most  of  the 
rain,  as  indicated  by  the  shading  ? 

Whence  comes  the  air  in  the  western  part  of  the  whirl — from 
northerly  or  from  southerly  regions  ? 

Will  it  probably  be  colder,  or  warmer  ?     Why  ? 

Make  a  forecast  for  Cincinnati  for  each  of  the  two  days. 

Make  forecasts  for  New  York,  Denver,  and  Chicago  for  the  third  day. 


COLLATERAL  READING  AND  REFERENCE. 

Grbely. — American  Weather— pp.  178-273. 

United  States  Weather  Bureau. — Daily  Weather  Maps. 


NOTES 

'  In  the  tropics  the  cloud-ring  rarely  exceeds  five  hundred  miles 
in  diameter,  and  tiie  circle  of  dangerous  winds  is  scarcely  more 
than  half  as  great.  In  higher  latitudes,  however,  the  diameter 
of  the  storm  increases.  The  wind  is  more  violent  in  tropical, 
and  less  severe  in  higher  latitudes. 

^The  direction  of  the  whirl  is  thought  to  result  from  the  con- 
flict of  winds  as  they 'approach  the  up-draught.  Of  all  the  cui-- 
rents  setting  toward  the  storm-centre,  the  northeast  Trade  Wind 
is  the  strongest.  As  it  approaches  the  storm-centi'e  it  is  opposed 
by  weaker  winds  from  the  north,  northwest,  and  west.  As  a  re- 
sult, the  Trade  Wind  is  bent  toward  the  east  and  forced  to  rotate 
in  the  manner  described. 

'  The  barometer  gives  first  warning  of  the  approach  of  the  cy- 
clone. During  the  few  days  preceding,  the  barometer  is  perliaps 
above  its  normal  heiglat  and  the  weather  pleasant  and  clear. 
Sooner  or  later  the  barometer  begins  to  show  signs  of  unsteadi- 


CYCLONIC   STORMS  263 

ness,  and  at  the  same  time  a  long,  low,  ocean  swell  becomes  per- 
ceptible. Possibly  a  streamer  or  two  of  cat-tail  clouds  pointing 
toward  the  zenith  is  seen  in  the  south  or  southwest,  and  a  whit- 
ish arc  near  or  on  the  horizon  indicates  the  bearing  of  the  cen- 
tre. In  a  few  hours  or  less  the  barometer  begins  to  fall — slowly 
at  first,  and  then  more  rapidly.  A  halo  gathers  around  the  sun 
or  the  moon  ;  the  ocean  swell  increases,  the  sky  grows  purple, 
and  fitful  i^ufTs  of  wind  come  from  the  north.  There  can  no 
longer  be  any  doubt  of  the  approaching  storm,  and  the  prudent 
master  has  already  made  everything  snug  and  ready  for  the  com- 
ing blow.  Soon  a  heavy,  mountamous  bank  of  cloud  looms  up 
from  the  horizon.  This  is  the  cloud-ring  that  marks  the  edge  of 
the  storm,  and  the  circle  of  dangerous  winds  is  not  far  away. 
Finally  the  wind,  already  very  squally,  bursts  into  a  gale,  and 
veers  to  the  northward,  and  soon  the  storm  is  on,  in  full  force. 
If,  by  any  means,  the  course  has  not  been  altered,  or  if,  through 
accident,  the  ship  is  carried  with  the  wind,  the  latter  will  in- 
crease to  hurricane  strengtli,  and  not  even  the  smallest  storm- 
sail  will  stand  against  its  force.  Soon,  in  almost  a  twinkling, 
the  wind  lulls  and  the  ship  is  in  the  eye  of  the  storm.  Then  the 
sky  alternates  between  inky  blackness,  with  terrific  down-pours 
of  rain,  and  moments  of  misty,  j'ellow  light.  Perhaps  half  an 
hour  passes,  and  the  opposite  side  of  the  cyclone  strikes  the 
vessel.  At.  that  moment  the  wind  again  bur.sts  upon  the 
ship  from  the  opposite  direction.  Nothing  but  the  stanchest 
vessel  can  ride  through  such  a  storm.  A  square-rigged  ship  is 
apt  to  have  her  yards  stripped  off,  even  if  the  masts  are  not 
snapped. 

*  The  accompanying  storm  curds  are  adapted  to  use  in  any 
cyclones  of  the  northern  hemisphere;  the  ui)per  diagram  is 
available  for  the  route  between  New  York  and  English  ports. 
The  small  arrows  fly  with  the  wind  ;  the  long  arrow  represents 
the  storm  track  through  the  belt  of  latitude  to  which  the  dia- 
gram applies.  For  West  Indian  hurricanes  note  that  the  storm 
track  recurves  as  follows  :  June  and  OctolH'r,  latitude  20°  to  2;J"; 
.luiy  and  Septemljer,  latitude  27°  to  2!»°  ;  August,  latitu<le  :{0°  to 
33°.  When  a  falling  barometer  and  other  signs  indicate  the  ap- 
proach of  a  cyclone,  select  the  diagram  that  applies  to  the  lati- 
tude and  plot  the  position  of  the  .ship  according  to  the  direction 
(A  the  wind.     In  low  latitudes,  for  instance,  the  wind  is  N  NK  ; 


264 


PHYSICAL   GEOGRAPHY 


the  vessel  is  then  in  the  position  that  is  sliown  on  the  lower 
diagram,  and  is  in  the  dangerous  semicircle.  If  possible  it  is 
best  to  lie-to  (on  the  starboard  tack),  and  observe  the  wind  ;  if 
{a)  it  freshens  loitlumt  shifting,  the  vessel  is  certainly  in  the 
storm  track.  In  this  ease  the  naviofator  keeps  off,  with  the  wind 
on  the  starboard  quarter,  holding  to  the  course,  (b)  If  it  shifts 
to  the  rifjfit,  the  ship  is  to  the  right  of  the  storm  track  and  should 

be  put  on  the  starboard  tack. 


0^  «/^;v: 


making  as  much  headway  as 
possible  until  obliged  to  lie-to. 
(c)  If  it  shifts  to  the  left,  the 
ship  is  on  the  left  of  the  storm 
track  and  should  be  brought 
about  until  the  wind  is  on  the 
starboard  quarter,  lying-to  on 
the  port  tack  if  necessary.  In 
scudding,  the  wind  should  be 
kept  always  on  the  starboard 
tack  to  run  out  of  the  storm. 
If  the  vessel  is  in  the  latitude 
where  the  cyclone  probably 
recurves  (according  to  the 
month)  the  middle  diagram  is 
applicable.  Suppose  that  the 
wind  is  S  E  ;  the  vessel  then 
has  the  position  marked  in 
the  middle  diagram.  It  is  on 
the  right  of  the  storm  track 
and  should  run  out  as  in  (6), 
pi'eviously  noted.  In  high  lat- 
itudes the  upper  diagram  is 
indicated.  Suppose  that  the 
wind  is  N  E.  The  ship  then  has  the  position  shown  to  the  left 
of  the  storm  track,  in  the  navigable  semicircle,  and  should  be 
brought  about  as  in  (c),  previously  noted.  In  any  case  oil  may 
be  used  to  prevent  the  waves  from  ]:)reaking  over  the  vessel. 

'  It  is  unstable  because  the  cold  air  is  resting  on  a  layer  of 
air  that  is  specifically  lighter,  and  when  the  latter  is  pressed  up- 
ward it  soon  develops  into  a  whirl.  Winter  cyclones  are  not 
confmed  to  definite  localities,  as  ai-e   tropical  cyclones,  and  in 


■^w  sw.  /s  sw. 
STORM  CARDS. 


CYCLONIC   STORMS  265 

comparison  with  the  latter  their  tracks  are  erratic.  Their  gen- 
eral direction  is  easterly,  however. 

^  In  very  many  cases  a  land-storm  may  originate  at  sea  and 
finally  end  somewhere  at  a  considerable  distance  inland.  Many 
West  Indian  hurricanes  sweep  into  the  Gulf  of  Mexico  and  thence 
into  the  Mississippi  valley.  On  the  other  hand,  there  are  many 
— perhaps  a  majority  of  north  Atlantic  storms — that  begin  far  in 
the  interior  of  the  continent.  In  many  instances  storms  have 
originated  somewhere  in  the  Pacific,  crossed  the  United  States, 
and  the  Atlantic,  finally  disappearing  in  the  interior  of  Eurasia. 
Many  of  the  cyclonic  storms  of  the  Pacific  Coast  of  the  United 
States  travel  southward  between  the  Coast  Range  and  Sierra  Ne- 
vada Mountains.  In  some  instances  the  storm  is  dissipated  in 
the  arid  region  to  the  southward,  but  occasionally  a  cyclonic 
disturbance  finds  enough  moisture  to  enable  it  to  pass  into  the 
Mississippi  Valley. 

'  Under  such  conditions  a  warm  wave  results.  Although  with 
respect  to  temperature,  the  difference  between  warm  waves  and 
normal  weather  is  not  so  great  as  that  between  cold  waves  and 
normal  weather,  yet  the  former  are  far  more  fatal.  In  all  the 
densely  populated  parts  of  the  country  the  advent  of  a  warm 
wave  is  marked  by  an  enormous  increase  in  the  death-rate.  Dur- 
ing several  warm  waves  that,  in  July,  1881,  covered  the  Missis- 
sippi Valley,  there  were  more  than  one  thousand  deaths  from 
sunstroke — probably  a  greater  number  than  have  resulted  from 
the  cold  waves  of  a  score  of  years.  Warm  spells  may  result  from 
other  cases.  The  typical  "  warm  Avave  "  is  the  result  of  settled 
conditions,  and  not  disturbances.  The  air  resting  upon  the  given 
area  without  being  disturbed  in  the  course  of  two  weeks  becomes 
intolerably  hot. 

'  A  cold  wave  that  occurred  in  January,  1888,  is  an  example 
of  the  effects  of  the  translation  of  cold  air  from  the  extreme 
north.  At  Helena,  Montan.i,  the  temperature  fell  fifty  degrees 
in  four  and  one-half  hours,  and  sixty-four  degrees  in  less  than 
eighteen  hours.  At  Crete,  Nebraska,  the  thermometer  fell  eigh- 
teen degrees  in  three  minutes.  This  wave  covered  almost  the 
whole  United  States,  carrying  freezing  weather  into  Florida, 
California,  and  southern  Texas.  In  March,  1887,  a  cold  wave, 
extending  along  the  valley  of  th(^  St.  I.awreuce  River,  wa« 
marked  by  a  fall  of  teuiperatiirr   ranging  from  fifty  to  seventy* 


266 


PHYSICAL   GEOGKAPHY 


one  degrees  in  twenty-four  hours.  In  Denver,  January  15,  1875, 
there  was  a  drop  in  temperature  of  forty-eight  degrees  in  one 
hour. 

» This  term  was  first  noted  in  the  recoi-ds  of  an  exploring  party 
which,  in  1747,  wintered  on  the  shores  of  Hudson  Bay,  at  a  place 
now  called  York  Factory.  It  was  introduced  as  a  technical  name 
into  the  weather  service  in  1876. 

"  General  A.  W.  Greely,  U.  S.  A.,  notes  twenty-five  tornadoes, 
in  which  the  aggregate  damage  reached  the  sum  of  $15,000,000, 
while  the  loss  of  life  was  nearly  fifteen  hundred.  Concur- 
rent with  a  storm  that  in  February  9,  1884,  crossed  the  United 
States,  there  were  sixty  distinct  tornadoes.     On  that  day  eight 

hundred  people 
were  killed,  twen- 
ty-five hundred 
were  wounded, 
and  more  than  ten 
thousand  build- 
ings were  de- 
stroyed. 

"  The  story  il- 
lustrated in  this 
cut  is  a  grewsome 
summary  of  hor- 
rors. The  house 
was  surrounded 
by  a  grove  of  trees. 
To  the  east  of  the  house  the  trees  were  felled  and  twisted  from 
right  to  left  ;  those  west  of  the  house  were  untouched.  The 
house  itself  was  demolished  and  the  debris  hurled  into  the  creek- 
bed  near  by.  When  the  tornado  cloud  swooped  down  upon  the 
house,  the  family  fled  for  their  lives,  but  unfortunately  in  the 
wrong  direction.  At  first  they  ran  northward,  a  direction  of 
safety.  Then,  one  after  another,  they  turned  eastward — first  a 
little  girl,  who  was  instantly  killed  ;  then  an  older  boy  and  a 
girl,  who  were  bruised  and  partly  stripped  of  their  clothing. 
The  mother  ran  directly  into  the  whirl  and  was  found  crushed 
and  mangled  against  the  trunk  of  a  tree.  The  father,  with  the 
babe  in  his  arm^,  had  reached  a  place  of  absolute  safety,  but  in 
his  fright  turned  eastward  and  ran  into  the  whirl.     They  were 


N 

FATHER 
AND    BABY/ 

/ 

<i.\«<^..P^oPLE: 

/ 

U1-. 

,^BOY^ 

w 

*■■., 

-^•x 

'•>. ..--,,-'; 

-'''    , 

1^1  RL 

■■>  MOTHER 

E 

B       N3'i 

v; 

^'■.    ' ' 

IMTCUEN 

4V 

a;     .■'  ■p' 

€lRL 

HOUSE 

'■'Vf^ 

^          s 

CYCLONIC   STORMS  267 

picked  up  by  the  wind,  thrown  several  hundred  feet,  and  instant- 
ly killed.  Ad  inspection  of  the  accompanying  illustration 
shows  that  the  safest  path  of  flight  is  toward  the  northwest  or 
the  southeast ;  to  the  southwest  or  the  northeast  is  one  of  the 
greatest  danger. 

"  In  1853  the  necessity  for  a  weather  bureau  was  urged  by 
Commander  M.  F.  Maury,  but  it  was  not  until  after  his  death 
that  systematic  land  observations  were  carried  out.  The  first 
organization  was  effected  by  General  Myer,  U.  S.  A.,  Chief  Signal 
Officer,  who  trained  the  rank  and  file  of  his  department  to  make 
weather  observations.  Since  that  time  the  Weather  Bureau  has 
been  attached  to  the  Department  of  Agriculture  and,  placed  in 
charge  of  its  Secretary.  Most  of  the  European  nations  have  es- 
tablished similar  bureaus,  and  daily  observations  are  made  on  all 
transatlantic  steamships.  So  complete  are  these  records  that 
.scarcely  a  storm  occurs  in  the  North  Atlantic  which  is  not  fol- 
lowed and  its  path  predicted  with  a  high  degree  of  probability. 
Flags  (or  sometimes  painted  cylindei-s  and  cones)  are  displayed  on 
public  buildings  in  nearly  every  town  in  the  United  States  and 
Euroi>e.  For  land  service  the.se  flags  are  commonly  used.  A 
square  white  flag  denotes  clear  weather  ;  a  blue  flag,  rain  or  snow. 
Temperature  is  indicated  by  a  triangular  blue  flag.  Above  the 
square  flag  it  denotes  higher  temperature  ;  below  the  square  flag, 
](jwer  temperature  ;  its  absence  denotes  no  change  in  tempera- 
ture. Whenever  the  temperature  falls  twenty  degrees  or  more 
(sixteen  degrees  in  the  northern  States)  if  the  mercury  sinks  as  low 
as  32°  (F.),  it  is  technically  a  cold  wave,  and  its  approach  is  indi- 
cated by  a  white  flag  containing  a  black  square.  It  is  commonly 
called  the  "black  flag."  A  fifth  flag  is  sometimes  employed  to 
indicate  local  storms.  For  the  benefit  of  mariners  a  Montldy 
I'ilot  Chart  for  the  North  Atlantic  is  published  by  the  United 
Stiites  Hydrographie  Office.  This  shows  storm  tracks  of  the  pre- 
ceding month,  and  the  position  of  ice,  fog,  floating  wrecks 
(called  "derelicts"),  and  other  ob.stacles,  for  the  current  month. 


CHAPTEE  XV 

ELECTEICAL    AND    LUMINOUS     PHENOMENA     OF    THE 
ATMOSPHERE 

Electkicity  is  a  form  of  energy  that  is  manifested 
chiefly  by  its  effects  ;  of  its  actual  nature  practically  noth- 
ing is  known.  The  laws  pertaining  to  it  are  fairly  well 
known,  however;  and,  like  most  of  the  other  forces  of 
nature,  it  is  a  most  useful  servant  when  under  intelligent 
control.  In  the  slender  thread  of  the  incandescent  light 
and  the  carbons  of  the  arc  light  it  appears  both  as  light  and 
intense  heat.  Passing  through  insulated  copper-wire  that 
surrounds  a  core  of  soft  iron,  it  converts  the  latter  into  a 
magnet,  and  thus  harnessed  it  becomes  a  generator  of  great 
power.  Electrical  energy  seems  to  be  a  form  of  motion, 
and  it  may  be  produced  by  motion.  It  is  manifest  not 
only  in  the  earth  and  the  air,  but  in  space  as  well. 

The  fundamental  laws  of  electrical  energy  are  not  diffi- 
cult to  understand.  If  a  pith-ball,  suspended  by  a  silk 
fibre,  be  brought  near  a  piece  of  hard  rubber,  or  vulcanite, 
that  has  been  briskly  rubbed  by  flannel,  the  ball  will  at 
first  cling  to  the  vulcanite  and  then  immediately  be  re- 
pelled from  it.  If  another  ball,  electrified  in  a  similar 
manner,  be  brought  near  the  first,  the  two  will  vigorously 
repel  each  other.^  If,  however,  the  second  pith-ball  be 
electrified  by  a  piece  of  glass  rubbed  with  silk,  the  two 
balls  Avill  then  show  a  strong  attraction  for  each  other. 

Such  an  experiment  demonstrates  the  principal  laws  of 
electricity.     Bodies  similarly  electrified  repel ;   bodies  dif- 

268 


ELECTRICAL   AND    LUMINOUS    PHENOMENA    269 

ferently  elecirijied  attract  one  another.  The  electricity  de- 
veloped when  glass  is  rubbed  with  silk  is  called  positive  ; 
that  produced  by  rubbing  vulcanite  with  jflannel,  negative. 
Electricity  passes  quite  freely  through  metallic  sub- 
stances, but  with  difficulty  through  such  material  as  silk, 
wool,  gums  and  resins,  dry  wood,  and  dry  air.  When, 
however,  the  electric  force  is  so  great  that  it  will  pass 
through  these  it  is  said  to  have  a  high  potential,  just  as 
steam  confined  within  a  boiler  is  at  high  pressure.^    The 


LIGHTNING 
From  an  instantaneous  photograph  by   IV.   F.  Cannon. 

"  sparks  "  produced  by  rubbing  sealing  wax  or  vulcanite 
with  flannel  are  of  moderately  high  potential. 

To  the  electricity  of  the  air  and  the  earth  many  of  the 
most  marvellous  phenomena  are  due.  In  the  simplest 
form  we  see  its  ejffects  when  tiny  sparks  result  from  rub- 
bing the  long  knap  of  Avoollen  cloth  or  the  fur  of  an  animal 
pelt ;  we  see  its  grandest  effects  Avhen  great  flashes  of  light- 
ning forge  across  the  sky.  The  electricity  of  the  air  is  usu- 
ally of  high  potential  ;   that  which  forms  a  flash  of  light- 


270  PHYSICAL   GEOGEAPHY 

ning  is  of  exceedingly  high  tension.  Next  the  earth, 
however,  the  electricity  of  the  atmosphere  is  not  commonly 
noticeable,  especially  if  the  air  is  moist.  At  considerable 
elevations,  or  at  times  when  the  air  is  very  dr}-,  its  pres- 
ence becomes  marked.  The  hair  of  the  head  crackles  as 
a  comb  is  drawn  through  it,  and  tiny  sparks  are  given  off 
when  woollen  clothing  is  rubbed.  In  the  dry  summer 
climate  of  deserts,  the  hair  of  horses'  tails  stands  out  like 
bushes,  and  their  manes  are  like  fright  wigs  ;  sparks  half 
an  inch  long  may  be  drawn  from  a  metallic  body  insulated 
from  the  ground. 

Ordinarily  the  electricity  of  the  air  is  positive,  but,  Avith 
much  moisture  present,  it  may  be  negative.  Just  before 
the  beginning  of  a  gentle  shower  it  often  becomes  nega- 
tive, and  during  a  heavy  storm  it  frequently  changes  from 
positive  to  negative  and  vice  versa  very  rapidly.  In  such 
cases  the  character  of  the  electricity  may  vary  in  different 
places ;  that  is,  it  may  be  positive  at  one  locality  and  neg- 
ative at  another,  only  a  few  miles  distant.^ 

Neither  physical  nor  chemical  change  in  a  substance 
takes  place  without  the  development  of  electric  energy. 
Friction  likewise  is  a  potent  factor  in  its  generation.  The 
flowing  of  water ;  the  chafing  of  the  winds  against  the 
earth's  surface  ;  even  the  friction  of  the  air  against  itself 
produces  it  copiously.  Evaporation  and  condensation  are 
attended  by  an  electric  disturbance ;  and  inasmuch  as  an 
enormous  amount  of  the  vapor  of  water  is  constantly  aris- 
ing from  the  earth  at  one  place  to  be  condensed,^  at  an- 
other these  changes  in  physical  form,  together  with  fric- 
tion, maybe  regarded  as  the  chief  agents  in  its  production. 

Since  these  factors  are  constantly  at  work,  it  is  evident 
that  electricity  is  being  constantly  produced.  But  the 
electricity  of  the  air  and  that  of  the  earth  are  unlike  ; 
the  two,  therefore,  neutralize  each  other.     Because  moist- 


ELECTRICAL   AXD   LUMIXOUS   PHENOMEXA    2T1 

m-e  is  a  good  conductor,  if  the  air  be  moist  the  two  kinds 
of  electricity  readily  pass,  one  from  the  earth  to  the  air, 
the  other  from  the  air  to  the  earth,  until  the  equilibrium 
is  restored.  This  transference  is  quietly  but  constantly 
going  on,  so  that  ordinarily  there  is  no  great  accumulation 
of  electricity.  It  is  only  when  the  air  is  very  diy  that 
the  transference  takes  place  with  difficulty. 

Thunder  Storms. — When  clouds  are  present  in  the 
air,  however,  there  is  often  an  enormous  accumulation  of 
electricity,  either  within  or  upon  their  surface,  and  the 
transference  or  exchange,  therefore,  may  become  violent 
and  destructive.  Such  disturbances  are  commonly  known 
as  thunder  storms. 

When  large  masses  of  cloud  hover  over  the  earth  it 
sometimes  happens  that  they  are  differently  electrified. 
Under  such  circumstances  the  two  clouds  are  mutually  at- 
tracted. The  potential  of  the  electricity  is  very  high  and 
the  transference  takes  place  in  the  form  of  blinding  flashes 
of  lightning.^  Usually  the  interchange  takes  place  between 
the  two  clouds,  but  not  infrequently  it  is  between  the 
clouds  and  the  earth.  The  form  of  lightning  varies.  The 
interchange  takes  place  always  along  the  line  of  least  re- 
sistance, and  as  this  is  seldom,  if  ever,  a  straight  line,  it 
has  taken  the  name,  zig-zag  lightning.^ 

Another  form  is  known  as  sheet  lightning.  This  inter- 
change takes  place,  not  along  a  line,  in  the  form  of  a 
chain,  but  simultaneously  over  a  large  area.  The  dis- 
charge is  not  attended  by  a  crash  of  thunder  nor  by  a 
blinding  flash  of  light.  On  the  contrary  there  is  nothing 
but  a  quivering,  bluish  glow  that  lasts  sometimes  for  eight 
or  ten  seconds.  A  sheet-lightning  discharge  takes  place 
usually  between  the  earth  and  the  clouds.  The  electricity  is 
of  low  potential  and  therefore  not  destructive.  This  name 
is  also  applied   to  flashes  of  lightning  that,  occurring  at 


272  PHYSICAL   GEOGRAPHY 

a  considerable  distance,  are  reflected  from  the  under  sur- 
faces of  clouds.'  Still  another  form  is  cominonlj  called 
hall  lightning.  Of  this  kind  of  discharge  but  little  is 
known,  and  although  its  occurrence  has  been  alleged  for 
more  than  two  hundred  years,  its  existence  is  somewhat  in 
doubt. 

Occasionally  the  discharge  takes  unusual  forms.  Among 
them,  but  rare  in  occurrence,  is  the  phenomenon  known  as 
St.  Elmos  fire.  This  discharge,  though  best  known  at  sea, 
is  also  occasionally  observed  on  land.  At  the  time  of  its 
occurrence  there  is  usually  a  considerable  electrical  disturb- 
ance, though  not  necessarily  a  thunder-storm.  Owing  to 
the  feebleness  of  the  light  emitted,  it  is  rarely  if  ever 
noticed  in  the  daytime.  It  consists  of  a  pale,  shimmering 
light,  at  the  tips  of  the  yards,  spars,  and  from  every 
pointed  part  of  the  ship's  rigging.  The  glow  lasts  for  a 
few  moments  and  then  the  phantom  light  disappears.^  In 
all  probability  the  St.  Elmo's  fire  is  identical  with  the 
bluish  glow  that  is  seen  when  a  frictional  electrical 
machine  is  worked  in  the  dark — a  phenomenon  commonly 
known  from  its  shape  as  the  "  brush  "  discharge. 

The  Aurora  Borealis.  —  This  magnificent  display, 
commonly  called  the  "  northern  lights,"  »  is  without  doubt 
an  electrical  phenomenon  that  possibly  is  similar  in  nature 
to  the  brush  discharge.  It  is  most  common  in  high  lati- 
tudes, though  it  is  occasionally  observed  between  latitudes 
30°  and  40°  N.  In  appearance  the  aurora  is  an  arch  of 
light  stretching  across  the  sky  fifteen  or  twenty  degrees 
above  the  horizon.  It  has  a  tremulous  motion,  and  the 
upper  streamers  sometimes  mount  to  the  zenith. 

In  color  the  aurora  varies  between  pale  green  and  crim- 
son. Sometimes  it  closely  resembles  a  green  curtain  edged 
and  lined  with  gold.  Auroras  are  most  frequent  during 
sun-spot  periods  ;  they  are   usually  coincident  with  mag- 


ELECTRICAL   AND   LUMINOUS    PHENOMENA    273 

netic  storms  also.  In  circiimpolar  regions  they  are  of 
daily  occurrence. '°  The  cause  of  auroras  is  not  with  cer- 
tainty known,  but  they  are  thought  to  be  an  exchange  be- 
tween the  electricity  of  the  atmosphere  and  that  of  the 
earth.  The  arch  of  the  aurora  nearly  always  surrounds 
the  earth's  magnetic  pole." 

Magnetism. ^ — A  bar  of  steel,  iron,  or  nickel,  or  a  piece 
of  lodestone '~  that  has  the  property  of  attracting  and 
holding  to  its  surface  small  pieces  of  similar  metals  is 
called  a  magnet.  Steel  retains  its  magnetism  permanently, 
and  for  all  practical  purposes  the  magnet  is  a  flat  bar  of 
polished  steel,  eight  or  ten  inches  in  length.  Sometimes, 
however,  it  is  bent  into  a  U-shaped  form  called  a  horse- 
shoe magnet. 

When  a  bar  of  steel  is  magnetized,  it  is  found  that  the 
magnetic  force  is  not  uniformly  distributed  throughout  the 
bar,  but  is  most  intense  at  or  near  the  ends.^^  These  are 
the  poles  of  the  magnet ;  they  are  designated  as  positive 
+  ,  and  negative  — ,  according  to  the  direction  they  take 
when  the  magnet  is  suspended  at  the  centre  of  gravity. 

If  a  slender  bar  of  ordinary  steel  be  susjiended  by  a  hair 
from  its  centre  of  gravity,  it  Avill  lie  indiflerently  in  any 
direction  in  which  it  is  placed.  If  the  bar  be  magnetized, 
however,  it  takes  new  properties.  It  no  longer  remains  in- 
differently in  any  position ;  on  the  contrary  it  turns  until 
its  direction  is  nearly  or  quite  north  and  south.  It  no 
longer  remains  balanced,  but  the  ii()rlli-i)ointing  end  dijjs 
toward  the  earth. 

If  now  another  bar  magnet  bo  brought  near  it,  the  latter 
shows  no  little  sensitiveness.  If  the  +  end  of  the  bar  be 
presented  to  the  +  end  of  the  suspended  magnet,  the  latter 
will  instantly  turn  away  ;  if  tin;  two  —  ends  be  brought  to- 
gether the  same  tiling  will  Ix;  notic^cd.  On  tli(!  contrary  if 
+  and  —  poles  be  brought  together  tiicy  aiv  strongly  at- 


274 


PHYSICAL   GEOGRAPHY 


tracted.  From  these  experiments  the  laws  of  magnetism 
are  deduced.  Like  magnetic  poles  I'epel  ;  unlike  poles  at- 
tract. Either  pole  of  the  magnet,  however,  will  attract 
alike  an  uuniagnetized  piece  of  iron  or  steel. 

It  is  upon  these  laws  that  the  whole  science  of  naviga- 
tion by  the  compass  depends,  for  the  earth  behaves  as  a 
magnet"  and  the  essential  part  of  the  mariner's  compass  is 
also  a  magnet. 

Magnetic  Variation. — The  earth's  magnetic  poles  are 
not  situated  at  the  geographical  poles.  The  magnetic  north 
pole  is  situated  Avest  of  Boothia  Land,  a  few  miles  north 
of  the  crossing  of  the  97th  meridian  and  the  70th  parallel. 


LINES  OF  EQUAL  MAGNETIC  VARIATION 


Its  position  is  not  fixed,  and  it  is  moving  in  a  westerly  di- 
rection.'^ The  position  of  the  magnetic  south  pole  is  not 
known,  although  roughly  approximated. 

Because  the  magnetic  poles  are  not  situated  at  the  geo- 
graphic poles,  it  is  evident  that  the  magnetic  needle  can 


ELECTRICAL   AXD   LIJMmOUS   PHEXOMEXA    275 

point  due  north  and  south  in  but  few  places.  In  the  ac- 
companying chart,  a  heavy  black  line  passes  through 
these  points.  This  line,  called  the  agonic,  is  the  line  of 
no  variation.  West  of  this  line  the  north-pointing  end  of 
the  needle  turns  toward  the  east,  and  east  of  it  it  swerves 
to  the  west.  Along  each  of  the  lighter  lines  the  needle 
has  the  same  deviation  at  all  points,  and  these  lines,  there- 
fore are  called  isogonics  or  lines  of  equal  variation.  This 
deviation  from  the  true  meridian  is  called  declination. 

Trace  the  course  of  the  line  of  no  variation. 

Besides  that  element  of  magnetic  force  that  causes  the 
needle  to  he  in  a  nearly  north-aud-south  direction,  there 
is  another  that  causes  it  to  dip  or  incline  one  end  toward 
the  earth.  This  is  called  the  vei-tical  force,  or  inclination. 
Along  an  irregular  line  passing  around  the  earth,  some- 
times north  of  the  equator  and  sometimes  south  of  it, 
the  needle  has  an  absolutely  horizontal  position.  North 
of  this  line  the  negative,  or  north-pointing  end,  dips 
toward  the  earth.  The  farther  the  observer  goes  north- 
ward, the  stronger  becomes  the  vertical  force,  and  when 
the  magnetic  north  pole  is  reached  the  needle  has  a  ver- 
tical position,  the  —  pole  being  next  the  earth. 

South  of  the  magnetic  equator,  or  aclinal,  the  conditions 
are  reversed.  The  +  pole  dips  more  and  more,  until,  at 
the  magnetic  south  pole,  the  needle  is  again  vertical  with 
the  +  pole  next  the  earth.  A  line  on  which  the  dip  is 
everywhere  the  same  is  called  an  isoclinal. 

Not  only  does  tlie  position  of  each  isogonic  vary  from 
time  to  time,  but  the  rate  of  variation  is  not  uniform  ;  even 
at  the  same  place  the  rate  varies  from  year  to  year.  In 
the  northwestern  part  of  the  "United  States  the  amount  of 
variation  is  at  ])res(Mit  fnnn  3'  to  7' ;  in  the  southwestern 
part  it  is,  at  ja-csent,  nothing  ;  in  the  eastern  and  cent  nil 
parts  it  varies  from  5'  to  3'. 


2:g  physical  geography 

The  deviation  from  the  true  geographical  meridian  also 
varies  from  day  to  day.  Most  of  these  variations  are 
periodical.  Some  are  daily,  some  monthly,  and  some 
yearly  ;  the}^  are  probably  caused  by  the  daily  rotation  of 
the  earth,  the  passage  of  the  moon,  and  the  annual  motion 
of  the  earth.  There  are  also  irregular  changes  in  variation 
which  cannot  be  accounted  for. 

Such  changes  in  variation  are  rarely  great ;  in  temperate 
and  in  low  latitudes  they  cannot  well  be  detected  except 
by  close  measurements.  In  the  vicinity  of  the  magnetic 
jjole,  however,  they  are  more  marked.  At  Point  Barrow 
and  at  Lady  Franklin  Bay,  during  a  period  of  twenty-four 
hours,  a  change  of  nearly  eleven  degrees  was  recorded. ^^ 

Magnetic  Storms. — Not  infrequently  the  irregular  vari- 
ations of  the  needle  are  so  violent  that  they  have  been 
called  magnetic  "  storms,"  and  during  the  progress  of  one 
of  these  disturbances  the  needle  is  in  a  constant  tremor. 
Magnetic  storms  seem  to  be  closely  associated  with  the 
spots  that  at  times  are  visible  on  the  surface  of  the  sun. 
The  sudden  formation  or  change  in  the  position  of  a  sun- 
spot  is  nearly  always  attended  by  great  magnetic  disturb- 
ances. The  period  when  they  are  most  frequent,  more- 
over, corresponds  to  the  j^eriod  when  sun  spots  are  most 
numerous.^^ 

The  Mariner's  Compass.— The  compass  is  a  slender 
bar  of  magnetized  steel,  so  constructed  as  to  balance  on  a 
pivot  and  turn  freely  upon  it  as  well.  Usually  it  is  armed 
with  a  sliding  weight,  so  adjusted  that  it  exactly  counter- 
balances the  dip  or  vertical  force,  thereby  keeping  the 
needle  in  a  horizontal  position. 

On  land  the  compass  is  of  but  little  practical  use  except 
in  rough  surveys.  On  the  sea,  however,  it  furnishes  the 
only  means  by  which  a  vessel  may  be  kept  continually  on 
her  course.     For  this    reason  the  mariner's   compass   is 


ELECTRICAL   AND   LUMINOUS   PHENOMENA    277 


constructed  with  the  greatest  care  and  precision.'^  The 
needle,  which  consists  of  one  or  more  slender  bars  of  steel, 
is  fastened  to  a  circular  card  subdivided  into  thirty-two 
parts,  on  which  are  printed  the  cardinal  directions.  These 
are  called  points  of  the  compass.  The  compass-box  is 
mounted  on  gimbals,  so  that,  no  matter  what  may  be  the 
motion  of  the  vessel,  the  box  always  swings  into  a  hori- 
zontal position. 

In  going  over  almost  every  travelled  ocean  route, 
the  variation  of  the  compass  changes  day  by  day.  On 
the  regular  routes  of  the 
transatlantic  liners,  the 
variation  increases  from 
about  eight  degrees  at 
New  York  to  more  than 
thirt^'-five  degi'ees  at  the 
crossing  of  the  40th  me- 
ridian. It  then  decreases 
to  about  twenty  degi'ees 
at  Liverpool. 

In  arctic  regions,  where 
the  horizontal  element  of 
force  is  so  weak,  and  the 
dipping  force  so  strong, 
sailing  by  compass  is  a  very  difficult  matter.  Not  only 
does  the  variation  change  rapidly  over  short  courses,  but 
the  needle  becomes  exceeding  sluggish.  On  whaling  ves- 
sels it  is  customary  to  attach  a  line  to  the  conipass-lH)x  so 
that  the  steersman,  by  occasionally  shaking  it,  may  Ix-tter 
judge  the  course  over  which  the  vessel  is  sailing. 

Luminous  Phenomena.— Transparent  as  it  seems,  the 
atmosphere  nevertheless  does  not  atford  passage  to  nil  llie 
light  that  may  be  transmitted  through  it.  A  ray  of  light 
in  passing  oblicpaely  is  not  only  refracted,  or  bent  out  of 


MARINER'S  COMPASS 
y4»;  nrditiary  pattern. 


278  PHYSICAL   GEOGEAPHY 

tliG  directiou  iii  which  it  started,  but  possibly  it  is  decom- 
posed into  differently  colored  rays.  The  distortion  that 
one  may  observe  by  looking  at  an  object  across  the  top  of 
a  very  hot  stove,  or  a  smoke-burning  chimney  is  an  ex- 
ample of  refraction.  On  the  other  hand,  the  color  effects 
observed  when  light  passes  through  a  glass  prism,  such  as 
a  chandelier  pendant,  or  even  the  bevelled  edge  of  plate- 
glass,  are  examples  of  decomposition — the  beautiful  dis- 
play of  the  colors  red,  green,  and  violet,  with  their  com- 
pounds resulting. 

A  ray  of  light  striking  the  surface  of  a  highly  polished 
metal  or  vitreous  substance  is  reelected,  rebounding  in  the 
same  manner  as  does  a  rubber  ball  thrown  against  the  floor. 
The  same  thing  occurs  when  the  ray  strikes  the  surface  of 
a  body  of  water,  or  even  that  of  two  layers  of  air  resting 
one  upon  the  other. 

The  air  always  contains  innumerable  dust-motes  and 
particles  of  matter  so  fine  and  light  that  they  seem  always 
to  float.  This  is  seen  when  a  few  rays  are  admitted  into  a 
darkened  room ;  the  passage  of  the  rays  is  marked  by  the 
light  reflected  by  the  motes ;  and  it  follows,  therefore,  that 
a  part  of  the  light  emanating  from  a  luminous  source  is 
always  scattered.  The  scattering  of  the  light  in  this 
manner  is  called  diffraction.  It  is  a  singular  fact,  more- 
over, that  some  kinds  of  floating  matter  will  scatter  the 
blue,  while  other  kinds  scatter  the  red  rays. 

The  color  of  the  sky  is  thought  to  result  from  diftrac- 
tion.  The  red  rays  are  scattered  and  the  blue  rays  ordi- 
narily reach  the  eye.  At  times,  however,  when  the  air  is 
heavy  with  dust,  the  sky  acquires  a  hue  that  is  distinctly 
red.  This  was  very  noticeable  in  1883,  after  the  eruption 
of  Krakatoa ;  for  nearly  a  year  the  sunsets  were  exceed- 
ingly lurid.  Ordinarily,  at  sea,  the  blueness  of  the  sky  is 
very  marked,  and  the  color  is  purer  than  on  land  ;  with  ac- 


ELECTEICAL   AND   LUMINOUS   PHENOMENA    279 

cumulating  moisture,  however,  it  may  acquire  purplish 
tiuts.  At  very  gi-eat  elevations,  also,  the  blue  gives  way 
to  a  dead  hue  that  approaches  blackness. 

Mirages. — When  a  layer  of  air  rests  on  another  of 
different  temperature  and  density,  the  surface  of  contact 
often  reflects  so  much  light  that  it  acts  as  a  mirror.  If  the 
surface  is  lower  than  the  eye  of  the  observer,  the  reflection 
much  resembles  that  produced  by  a  body  of  water,  and  a 
mirage  results.  In  deserts  and  arid  regions,  the  illusion  is 
so  perfect  that  nothing  but  experience  will  enable  one  to 
distinguish  the  mirage  from  a  lake.  The  "  lake  "  mirages 
of  the  Colorado  Desert  have  hired  both  cattle  herds  and 
travellers  to  their  death. 

With  the  reflecting  surface  above  the  eye,  the  character 
of  the  mirage  differs.  Thus,  at  times,  oft'  the  lake  shore 
at  Chicago,  one  may  see  the  lighthouse  and  the  shipping  at 
the  mouth  of  the  river  inverted  in  the  air.  If  possible, 
illustrate  this  by  means  of  a  large  mirror  held  overhead, 
face  downward. 

Still  another  form  of  mirage  occurs  when  objects,  ordi- 
narily hidden  by  the  earth's  curvature,  are  brought  in 
sight.  It  sometimes  happens  that  the  rays  of  light  reflect- 
ed from  an  object,  are  refracted  so  that  they  are  curved 
slightly  toward  the  earth,  and  a  distant  object  is  thereby 
brought  to  view.  This  phenomenon  occurs  at  times  rdong 
the  Mediterranean  and  Red  Seas,  and  it  is  not  unknown 
along  the  Great  Lakes.  As  a  rule,  a  dry,  still  atmosphere 
is  essential  to  tlie  formation  of  the  mirage. 

Coronas  and  Halos.— The  ring  or  rings  about  the  sun 
or  the  moon  are  very  common  phenomena.  The  small 
rings  are  coronas  ;  tlie  larger  ones,  halos.  In  tlie  case  of 
the  corona,  which  is  not  of  very  common  occurrence,  there 
is  usually  a  series  of  concentric,  colored  rings.  Those,  it 
is  thought,  result  from  diffraction,  the  light  being  scattered 


280  PHYSICAL   GEOGRAPHY 

by  the  moisture  of  the  atmosphere.  The  halo  arouud  the 
moon  is  probably  caused  by  refraction,  aud  it  appears 
when  the  air  is  very  moist.  For  this  reason  it  is  apt  to 
portend  rain  or  snow. 

The  halos  of  the  sun,  which  are  associated  usually  with 
cold  weather,  probably  are  caused  by  the  refraction  of  the 
light  as  the  latter  passes  through  the  ice  crystals  of  cirrus 


HALOS   OBShKVHD   BY   GENERAL    GREHLY 

clouds.  Frequently  there  are  several  circles.  Some  of 
them  are  concentric  ;  some  are  tangent  one  to  another  ; 
and  some  intersect  one  another.  At  the  places  of  inter- 
section and  of  tangency  more  light  is  radiated,  and  these 
spots,  therefore,  are  sometimes  very  bright ;  they  form  the 
sun  dogs,  or  Tnoch  suns. 

Rainbows. — Occasionally,  during  a  summer  shower, 
when  the  sun  breaks  through  a  rift  in  the  clouds,  the  light 
passes  through  the  falling  drops  of  water  in  such  a  way 
that  it  is  not  only  refracted  but  decomposed.  The  resulting 


ELECTRICAL  AND   LUMINOUS   PHENOMENA    281 

decomposition  is  the  arch  of  colored  light  that  constitutes 
the  rainbow.  The  bow  is  blue  and  violet  on  the  inner,  and 
red  on  the  outer  side.  Sometimes  there  is  a  larger  second- 
ary box  in  which  the  order  of  colors  is  reversed. 

The  rainbow  is  best  observed  when  the  sim  is  near  the 
horizon.  The  observer  sees  the  bow  when  his  back  is 
turned  toward  the  sun.  The  rainbow  is  frequently  ob- 
servable when  heavy  waves  break  and  send  spray  high 
into  the  air,  and  also  in  the  ascending  spray  of  cascades. 

QUESTIONS  AND  EXERCISES.— Verify  the  statements  concern- 
ing the  mutual  attraction  and  repulsion  of  electrified  bodies,  observing 
the  directions  contained  in  note  i. 

Verify  the  statements  concerning  the  laws  of  magnetism  noted  on 
p.  273,  using  one  or  more  stout  knitting-needles  and  strands  untwisted 
from  silk  thread.  For  observing  inclination  the  strand  of  silk  had 
better  be  fastened  by  means  of  a  slip  knot  to  the  needle  ;  for  the  other 
experiments  the  needle  may  be  thrust  through  a  bit  of  pap«r  to  which 
the  silk  is  attached.     In  magnetizing  the  needles,  rub  the  ends  only. 

From  the  chart,  p.  274,  estimate  the  magnetic  variation  of  the  place 
in  which  you  live. 

At  any  time  of  their  occurrence  note  carefully  whatever  you  may  ob- 
serve with  reference  to  auroras,  mock  suns,  halos,  and  coronas. 

Observe  whether  halos  of  the  moon  are  followed  by  clear  or  by  rainy 
weather. 

Occasionally,  in  very  dry  weather  the  disc  of  the  sun  is  considerably 
distorted  at  the  time  of  setting  ;  explain  why. 

Explain  the  cause  of  redness  that  occasionally  marks  sunrise  and  sun- 
set when  the  air  is  smoky. 

The  sun  and  the  moon  seem  to  be  much  larger  when  near  the  horizon 
than  at  zenith  ;  is  this  phenomenon  real  or  apparent  ?  The  use  of  a 
paper  or  other  tube  an  inch  or  two  in  diameter  will  aid  in  the  solution 
of  this  question. 

Explain  the  phenomenon  of  the  "  sun's  drawing  water." 

COLLATERAL   READING  AND   REFKRKNCE. 

Waldo. — ElemciitK  of  Mcteorolof^y  -  pp.  KKJ-IBO. 
fiKKKl>Y. — Aiii('ri(!Jin  Wc^iither. 
Davis— Elements  of  Meteorology. 


382  PHYSICAL   GEOGRAPHY 


NOTES 

*  Small  pieces  of  cork  will  answer  for  these  striking  experi- 
ments, but  bits  of  alder  pith  are  better.  In  order  that  they  may 
be  successful  the  air  of  the  room  should  be  very  dry.  The  pith- 
balls  may  hang  from  the  end  of  a  penholder  thrust  obliquely 
into  the  coi'k  of  a  stoppered  bottle.  For  the  eleetriflers,  a  glass 
lamp  chimney  and  a  vulcanite  comb  may  be  used.  Each  must 
be  made  absolutely  clean,  as  the  slight  film  of  grease  from  the 
hands  will  interfere  with  the  reaction. 

^  The  potential  of  electricity  may  be  also  likened  to  pressure  on 
water  flowing  through  a  pipe.  If  the  pressure  be  low  the  water 
will  flow  quietly  through  the  pipe  and  fall  at  no  great  distance 
from  the  end  of  the  nozzle  ;  on  the  contrary,  if  the  pressure  be 
great,  it  will  be  projected  to  a  considerable  distance.  In  a  single 
cell  of  galvanic  battery  the  potential,  about  one  or  two  volts,  is 
so  low  that  the  electricity  will  not  jump  across  a  space  of  one 
thousandth  of  an  inch  ;  the  quantity,  moreover,  is  very  small. 
In  an  electric-light  wire  a  current  of  considerable  volume  will 
leap  across  a  space  one-tenth  of  an  inch  or  more  ;  its  potential 
is  about  1,000  to  1,500  times  as  great  as  that  found  in  a  cell  of 
an  ordinary  galvanic  battery,  being  from  2,000  to  5,000  volts.  A 
good  frictional  electric  machine  will  cause  sparks  to  leap  between 
points  ten  or  twelve  inches  apart ;  the  potential  is  very  high,  but 
the  quantity  is  small.  During  a  thunder-storm  a  stroke  of  light- 
ning may  jump  a  distance  of  a  mile.  Not  only  is  the  quantity 
enormous,  but  the  potential  is  so  great  as  to  be  immeasurable  by 
ordinary  standards. 

'  At  different  localities,  the  character  of  the  electricity  may  be 
so  very  unlike,  that  the  earth  currents  are  sufficient  to  operate 
telegraph  wires  without  the  aid  of  the  batteries.  In  regions  of 
dry  climate  such  conditions  are  more  frequent  than  in  areas  of 
considerable  rainfall. 

'  The  vapor  of  water  is  not  only  a  good  conductor  of  electricity, 
but  it  is  an  excellent  storage  reservoir  as  well.  The  small  glob- 
ules of  vapor  that  compose  the  cloud  mass  carry  each  the  charge 
of  electricity  upon  the  surface.  But  when  a  great  number  of 
these  globules  are  condensed  to  form  a  drop  of  water,  the  surface 
of  the  drop  is  infinitely  smaller  than  the  aggregate  surface  of  the 


ELECTRICAL   AND    LUMINOUS   PHENOMENA    283 

globules.  The  potential  of  the  drop,  in  comparison  with  that  of 
the  globules,  is  enormously  increased.  If  an  electrified  body,  such 
as  a  vulcanite  rule,  is  brought  near  a  sprayer  or  a  sprinkler  the 
fine  spray  immediately  gives  place  to  large  drops. 

'The  lightning  itself,  or  rather  the  electricity,  is  not  necessarily 
visible.  The  flash  of  light  that  accompanies  the  discharge  is 
due  to  some  extent  to  the  foreign  matter  in  the  path  of  the  dis- 
charge, heated  to  whiteness.  The  air  being  a  poor  conductor 
offers  considerable  resistance  to  the  passage  of  the  electricity, 
and  is  therefore  intensely  heated  along  the  line  of  discharge. 
The  thunder  is  produced  in  exactly  the  same  manner  as  is  the 
noise  that  accompanies  the  discharge  of  a  firearm.  The  air  at 
the  point  of  discharge  is  I'arefied  almost  to  the  extent  of  Vieing  a 
vacuum  ;  the  rush  of  the  air  to  fill  the  suddenly  made  vacuum 
is  accompanied  by  noise.  The  rumbling  of  the  thunder  is  due 
partly  to  echo  and  reverberation,  and  partly  to  the  fact  that  the 
sound  along  the  line  of  discharge  reaches  the  ear  at  different  in- 
tervals— the  greater  the  distance  the  longer  the  time  I'equired  for 
the  sound  to  reach  the  ear.  Discharges  of  high  potential  only  are 
accompanied  by  thunder. 

^  In  paintings  and  illustrations  it  has  always  been  customary 
to  depict  the  electric  discharge  in  the  foi'm  of  a  zigzag  line  of 
many  sharp  angles.  In  the  past  few  years  photographs  of  the 
lightning  stroke  have  been  successfully  made.  One  of  these  on 
a  preceding  page  shows  the  fallacy  of  former  notions  on  the 
subject. 

'  This  reflection  is  called  Iteat  lightKiag.  It  is  rarely  ever  ob- 
served except  at  the  horizon  when  the  latter  is  overcast  by  clouds. 
The  reflected  flashes  of  light  are  usually  so  far  away  that  the 
accompanying  thunder  is  not  heard. 

^  While  Caisar  was  engaged  in  carrying  on  his  military  opera- 
tions in  Africa,  he  relates  that,  during  a  severe  hail -storm,  the 
spears  of  his  fifth  legion  were  tipiK'd  with  fire.  The  phenomenon 
was  undoubtedly  identical  with  that  of  St.  Elmo's  fire.  It  is  not 
improbable  that  the  "  ignis  fatuus,"  "Jacko'  lantern,"  or  "Will 
o'  the  wisp"  is  a  similar  electric  phenomenon.  This  is  u  hazy 
indistinct  light  that  appears  occasionally  in  swamps.  According 
to  tradition  and  fiction,  the  ignis  fatuus  is  a  bright  light  that 
moves  ra[)i(lly  innn  placid  to  place  mainly  for  the  purpoi^c  of  allur- 
ing unsuspecting  travellers  into  dangerous  places.     Asamafl<T 


384  PHYSICAL   GEOGRAPHY 

of  fact,  it  has  no  great  power  of  locomotion,  and  practically  is 
stationary. 

"  The  aurora  is  not  confined  to  northern  regions  ;  it  occurs  in 
southern  circumpolar  regions  as  well.  In  the  southern  hemi- 
sphere, however,  it  is  called  the  aurora  australis,  but  the  south- 
ern aurora  is  neither  so  brilliant  nor  so  frequent  in  occurrence 
as  that  of  the  northern  regions. 

■"  It  must  not  be  thought  that  the  aurora  occurs  at  night-time 
only  ;  it  may  take  place  at  any  time — day  or  night.  It  is  not 
visible  in  day-time,  however,  on  account  of  the  greater  brilliance 
of  the  sun. 

"  Professor  Balfour  Stewart  has  advanced  the  opinion  that 
both  auroras  and  earth  currents  are  secondary  currents  due  to 
small  but  rapid  changes  in  the  earth's  magnetism.  The  body  of 
the  earth  may  be  compared  to  the  magnetic  core  of  an  induction 
coil,  the  lower  strata  being  the  insulating  medium,  while  the 
upper  strata,  which  are  much  better  conductors,  take  the  part  of 
a  secondary  coil. 

''  Nearly  all  the  elements  are  more  or  less  sensitive  to  magnet- 
ism ;  iron,  cobalt,  and  nickel  possess  the  force  most  strongly, 
however.  Bismuth  and  copper  seem  to  be  repelled  and  take  an 
east-and-west  position,  or  a  dii'eetion  at  right  angles  to  that  of 
an  ordinary  magnet.  Such  substances  are  said  to  be  diamagnet- 
ic.  A  piece  of  soft  iron  retains  its  magnetism  only  while  it  is  in 
contact  with  a  magnet  or  near  to  it ;  a  piece  of  steel,  on  the  con- 
trary, once  magnetized  retains  the  property  permanently.  A  steel 
bar  may  be  magnetized  by  rubbing  its  ends  with  those  of  another 
magnet,  or  by  winding  several  hundred  turns  of  insulated  wire 
about  it,  through  which  a  current  of  electricity  is  passing. 

"  If  the  bar  be  a  long  one,  or  if  the  quality  of  the  steel  is  not 
uniform,  there  are  usually  several  supplemental  poles  scattered 
about  the  surface.  For  the  same  reasons  a  light  slender  bar  is 
better  than  a  stout  one. 

'■'  The  shape  of  the  earth  is  not  such  that  its  magnetic  force  can 
possess  much  intensity.  Several  magnetic  poles  are  known  to  ex- 
ist, but  only  the  two  north  poles  of  great  intensity  are  usually 
charted.  The  pole  of  greatest  intensity  is  the  one  commonly 
known  as  the  magnetic  north  pole.  Since  its  discovery  by  Ross, 
it  has  moved  about  forty  miles  westward.  In  1879  it  was  ap- 
proximately located  by  Lieutenant  Schwatka  in  the  open  space 


ELECTEICAL  AND   LUMINOUS   PHENOMENA    285 

between  Victoria  and  Franklin  Straits.  Its  exact  position  has 
not  been  determined  since  1831,  and  it  is  doubtful  if  its  location 
at  that  date  was  so  precise  as  might  be  inferred  from  the  figures, 
which  are  expressed  in  minutes  of  arc.  At  that  time  there  were 
no  instruments  sufficiently  delicate  for  such  precise  determina- 
tion. In  1884  the  position  of  this  pole  was  again  approximately 
determined  to  be  in  lat.  70°  30'  N.  ;  long,  9(5°  40'  W.  The  po- 
sition of  the  magnetic  south  pole  has  not  been  with  certainty 
discovered. 

""  Observations  made  at  Paris  on  the  movement  of  the  magnetic 
north  pole  cover  a  period  of  more  than  three  hundred  years.  In 
1580,  the  declination  at  the  city  was  11°  30'  East.  It  decreased 
until  in  1683  it  was  nothing,  after  which  time  the  variation  be- 
came west.  The  westerly  variation  increased  until,  in  1814,  it 
amounted  to  about  22°  30'  W.  Since  that  time  it  has  dropped  to 
about  22°,  and,  it  is  thought,  is  slowly  decreasing.  In  1790  the 
variation  at  Norfolk,  Va.,  was  nothing  ;  in  1893  it  was  about  3° 
16'  W.  In  New  York  City  the  variation  in  1686  was  9°  W.  ;  in 
1790  it  had  decreased  to  4°  15'  W. ;  after  this  time,  however,  it 
gradually  increased  until,  in  1893,  it  was  about  8°  25'  W. 

'*  In  order  better  to  study  these  variations,  magnetic  observa- 
tories have  been  established  in  various  parts  of  the  world.  The 
essential  part  of  such  an  observatory  is  a  series  of  magnets  each 
carrying  a  small  mirror,  mounted  in  such  a  manner  that  a  spot 
of  light  is  thrown  on  a  sheet  of  photographic  paper.  The  sheets 
of  paper  are  fastened  each  to  a  cylinder  revolved  by  clockwork, 
so  that  the  spot  of  light  traverses  the  whole  length  of  the  sheet 
in  twenty-four  hours,  thus  drawing  a  line  upon  it.  If  the  mag- 
net were  motionless  the  line  would  be  straight,  but  if  the  mag- 
net turns  even  a  small  fraction  of  a  minute,  the  spot  is  thrown 
out  of  position  and  the  line  becomes  irregular.  Usually  three 
magnets  are  employed — one  to  mea.sure  variations  in  horizontal 
force  ;  one  for  variations  in  vertical  force  ;  and  one  to  measure 
the  strength  of  the  horizontal  force. 

"  This  period  recurs  every  eleven  years.  In  1882  the  formation 
of  a  sun  spot  was  attended  by  a  magnetic  storm  that  was  recorded 
at  Point  Barrow,  Lady  Franklin  Bay,  Los  Angeles,  Kew  (London), 
Cape  Horn,  and  Paris.  Telegraph  instruments  were  afTected,  and 
in  some  instances,  long  circuits  were  worked  by  ground  currents. 
At  the  magnetic  observatory  tlu-n    in  Los  Angeles,   Californi.i. 


286  PHYSICAL   GEOGKAPHY 

the  trtiuior  of  the  magnets  was  so  great  that  for  several  hours  one 
of  the  instruments  failed  to  make  a  legible  record. 

'"  in  the  Ritchie  compass,  now  generally  used  in  the  United 
States  Navy,  the  compass-box  is  tilled  with  alcohol  in  which  the 
card  and  needle  almost  float.  The  object  being  to  relieve  the 
bearing  of  the  weight  of  the  card,  and  thus  make  the  needle  more 
sensitive.  It  is  a  most  excellent  compass  and  is  vastly  superior 
to  the  ordinary  compass  formerly  used.  The  compass  of  Sir 
William  Thomson  (Lord  Kelvin),  consists  of  a  battery  of  six  or 
more  vei"y  slender  magnets  held  in  a  skeleton  frame.  The  latter 
is  so  light  that  the  friction  on  the  bearing  is  imperceptible.  This 
compass  is  used  in  the  English  Navy,  and  by  most  of  the  trans- 
atlantic liners.  As  an  efficient  instrument  it  has  no  superior. 
The  use  of  steel  in  the  construction  of  vessels  has  added  materi- 
ally to  the  difficulties  of  sailing  by  compass.  The  hull  of  a  steel 
or  iron  vessel  has  poles  of  intensity  peculiar  to  itself,  and  these 
iire  apt  to  change  in  time,  so  that  frequent  tests  of  the  compasses 
are  necessary.  There  are  various  devices  for  obtaining  the 
proper  correction  for  the  compass  on  steel  vessels ;  a  very  effec- 
tive method  is  to  swing  the  vessel,  stem  and  stern,  along  a 
geographic  meridian  and  then  compare  the  observed  with  the 
normal  variation.  On  battle-ships  either  the  addition  or  the 
removal  of  the  armament,  or  the  substitution  of  a  steel  for  a 
wooden  mast,  is  apt  to  make  readjustment  of  the  compasses 
necessary. 


CHAPTEK  XVI 

CLIMATE  AND   ITS   FACTORS 

The  conditions  of  a  region  with  reference  to  its  liabita- 
bility  constitute  its  climate,  and  these,  in  general,  are  the 
results  of  heat  and  moisture  ;  climate,  therefore,  includes 
all  the  modifications  of  environment  due  to  heat  and  cold, 
rain  and  drought.  It  is  modified  by  many  conditions,  of 
which  the  principal  are  latitude,  altitude,  position  of  high- 
lands, direction  and  prevalence  of  winds,  and  the  inclina- 
tion of  the  earth's  axis,  together  with  its  constant  parallel- 
ism to  itself.' 

Latitude. — Latitude  affects  climate  chiefly  with  refer- 
ence to  temperature.  The  greater  the  distance  from  the 
equator,  the  lower  will  be  its  average  temperature.  The 
sun's  rays  are  never  vertical  beyond  the  tropics,  and  in 
polar  regions  they  fall  so  obliquely  that  they  impart  but 
very  little  heat  to  the  surface  which  they  strike.  Illustrate 
this  by  means  of  the  diagi'am  on  p.  294. 

In  going  from  the  equator  to  polar  regions,  therefore, 
one  will  pass  through  about  every  degree  of  warmth  from 
perpetual  summer  to  the  coldest  winter.  AVithin  thirty 
or  thirty-five  degrees  of  the  equator  the  change  in  tempera- 
ture is  not  great,  l)ut  beyond  the  forty-fifth  ])arall('l  the 
winter  climate  grows  rapidly  cooler  for  cv(n-y  few  degrees 
of  increase. 

Latitude  also  exerts  a  considerable,  inflnenco  on  rainfall. 
As  a  rule  the  rainfall  is  greatest  within  the  torrid  zone. 

387 


288  PHYSICAL   GEOGRAPHY 

lu  the  region  of  tropical  calms,  on  the  contrary,  the  rainfall 
is  usually  deficient.  These  calms  are  regions  of  descend- 
ing currents  of  the  air,  and  the  air  being  warmed  by  its 
descent,  instead  of  chilled,  but  little  rain  falls. 

Altitude. — The  effect  of  altitude  is  much  the  same  as 
that  of  latitude.  On  an  average  the  temperature  is  lower 
by  about  one  degree  for  every  three  hundred  feet  of  ascent. 
Thus,  even  in  equatorial  regions,  one  may  find  on  the 
slopes  of  suow-clad  highlands  all  the  intermediate  degrees 
of  temperature  between  perpetual  summer  and  eternal 
winter.  In  Mexico  the  effects  of  altitude  are  finely  illus- 
trated. The  city  and  seaport,  Vera  Cruz,  is  intolerably 
hot  and  moist,  yet  less  than  two  hundred  miles  away,  the 
City  of  Mexico  enjoys  a  climate  that  is  dry,  cool,  and  in- 
vigorating. The  difference  is  due  almost  wholly  to  its  alti- 
tude— about  7,000  feet  above  the  sea-level. 

A  still  more  striking  example  is  found  among  the  pla- 
teaus of  the  Colorado  River.  Hurricane  Ledge  is  an 
almost  vertical  escarpment,  2,500  feet  high,  that  forms 
the  boundary  between  two  plateaus.  On  the  upper  mesa 
the  products  are  those  of  a  temperate  climate  ;  in  the 
lower  they  are  distinctly  sub-tropical.  It  is  scarcely  more 
than  a  stone's  throw  from  the  former  to  the  latter. 

Position  of  Mountains. — The  existence  of  high  moun- 
tain-ranges often  determines  the  quantity  of  rain  precip- 
itated upon  the  surface  of  a  given  region.  In  tropical  lati- 
tudes rain-bearing  winds  blow  from  the  east,  and  the  eastern 
slopes  of  high  ranges  are  therefore  well  watered,  while 
the  western  slope  is  dry.  In  the  temperate  zones,  on  the 
other  hand,  the  rain  winds  are  from  the  west ;  and  the 
western  slopes  in  consequence  receive  most  of  the  rain, 
while  the  eastern  side  is  comparatively  dry.  Thus,  in  the 
Peruvian  Andes,  the  rain  winds  deluge  the  eastern  slope, 
leaving  the  western    side  practically  a  desert.      In    the 


CLIMATE   AND   ITS  FACTORS         '       289 

southern    Andes,  the  conditions  are    reversed ;    the    rain 
falls  on  the  western  side  while  the  eastern  slope  is  arid. 

The  effect  of  the  absence  of  mountains  is  observable  in 
Australia.  Partly  because  of  its  latitude,  but  mainly  for 
want  of  a  high  range,  the  greater  part  of  the  continent  is 
a  desert,  and  about  the  only  rain  that  falls  is  precipitated 
on  the  highlands  of  the  eastern  side.  In  the  great  African 
desert,  the  few  isolated  ranges  receive  considerable  rain 
on  their  summits,  but  none  falls  elsewhere. 

Distance  from  the  Sea. — The  proximity  of  the  sea 
exerts  a  marked  effect  on  climate,  both  with  respect  to  tem- 
perature and  moisture.  The  climate  of  a  coast  region  is 
always  more  equable  than  that  of  a  far  inland  or  continental 
area.  The  reason  therefor  is  apparent ;  the  air  over  the 
ocean  has  a  much  more  uniform  temperature  than  that 
over  the  land.  The  result  is  seen  Avhen  the  extremes  of 
temperature  are  noted.  For  example,  San  Francisco  and 
Leavenworth,  Kan.,  have  nearly  the  same  mean  temper- 
ature for  the  year.  But  while  the  difference  between  the 
summer  and  winter  temperature  of  San  Francisco  is  less 
than  ten  degrees  (F.),  that  of  Leavenworth  is  almost  fifty 
degrees.^ 

Not  all  coast  regions,  however,  enjoy  a  maritime  climate. 
Because  the  winds  of  the  temperate  zones  are,  as  a  rule, 
westerly,  in  the  eastern  coast  of  such  regions  land  winds 
are  prevalent.  The  coast  region  of  the  northeastern  part 
of  the  United  States  is  an  example.  Its  climate  is  dis- 
tinctively continental,  and  the  influence  of  the  sea  pene- 
trates only  a  very  few  miles  inland. 

The  climate  of  islands  at  a  distance  from  any  largo  body 
of  land  is  always  equable.  The  Philippines  and  the  Ha- 
waiian Islands  are  examples  ;  although  in  the  torrid  7x)no, 
they  are  regions  of  perpetual  spring,  with  no  excesses  of 
temperature.     The  Leeward  and  Windward  islands  of  the 


390  PHYSICAL   GEOGRAPHY 

West  Indian  group  are  also  examples.  Though  situated 
only  a  few  degrees  north  of  the  eqiiator  their  summer  tem- 
perature is  less  oppressive  than  that  of  New  York  City. 

Prevailing  Winds. — Winds  are  the  chief  medium  for 
the  transmission  both  of  moisture  and  warmth.  Cold 
winds  from  polar  regions  modify  the  excessive  heat  of  low 
latitudes,  and  tropical  winds  blowing  into  high  latitudes 
soften  the  rigors  of  polar  climate.  The  mild  temperature 
of  western  Europe  is  due  largely  to  southwesterly  winds, 
and  the  same  is  true  of  the  equable  climate  of  western 
North  America.  Not  only  do  the  winds  themselves  trans- 
fer a  great  amount  of  heat  by  convection,  but  the  vapor  of 
water  furnishes  an  enormous  supply.  For  every  pound  of 
water  vaporized,  enough  heat  is  made  latent  to  raise  nearly 
half  a  ton  of  water  one  degree  (F.)  in  temperature.  When 
the  vapor,  mingled  with  the  wind,  is  carried  to  higher  lati- 
tudes and  there  precipitated,  all  this  heat  is  again  set  free. 
An  inspection  of  the  chart  of  winds  (p.  221)  readily  gives 
all  the  information  necessary  to  determine  roughly  the 
climate  of  a  country.  The  regions  invaded  by  sea  winds 
that  have  come  from  low  latitudes  are  the  regions  of  Avarm 
and  equable  climate.  Inland  and  polar  regions  are  areas 
of  climatic  extremes. 

Changes  in  Climate. — As  a  rule,  the  climate  of  a 
country  is  constant ;  that  is,  it  does  not  change  materially 
except  after  long  intervals  of  time.  The  mean  tempera- 
ture of  any  given  locality  rarely  varies  more  than  a  very 
few  degrees  from  one  year  to  another,  and  the  averages  of 
long  periods  show  still  less  variation.  Fluctuations  in  rain- 
fall and  cloudiness  are  considerably  greater  than  those  of 
temperature.  In  regions  of  generous  rainfall  the  precipi- 
tation of  very  wet  years  may  be  nearly  twice  that  of  very 
dry  years,  but  in  localities  of  deficient  rainfall  the  differ- 
ence may  be  greater. 


CLIMATE   AND  ITS   FACTORS  291 

When  time  is  reckoned  by  geological  epochs,  however, 
it  seems  certain  that  great  climatic  changes  have  occurred 
in  every  part  of  the  earth,  and  that  they  have  been  of  the 
most  radical  character.  The  Glacial  Epoch,  already  de- 
scribed, is  an  example  of  a  change  in  the  climate  that  has 
taken  place  in  the  North  Temperate  Zone.  It  is  certain 
that  the  rainfall  of  the  Basin  Region  of  the  United  States 
is  subject  to  periods  of  oscillation.  The  few  scattered 
sinks  and  salt  lakes  of  the  Great  Basin  itself  are  remnants 
of  two  large  lakes  that  existed  there  at  no  very  remote 
period,  and  these  in  turn  are  evidence  of  a  much  greater 
rainfall  than  the  region  receives  at  the  present  time. 

Definite  knowledge  of  such  changes,  in  the  main,  is  cir- 
cumstantial, and  statistics  regarding  them  are  almost 
wholly  wanting.  The  cause  or  causes  of  such  changes, 
moreover,  are  unknown.  A  change  in  the  inclination  of 
the  earth's  axis  would  be  competent  to  account  for  changes 
in  temperature,  and  therefore  in  rainfall.'^  Changes  in  in- 
clination have  certainly  occurred,  but  their  definite  ell'ects 
are  not  known.  Changes  in  the  level  of  a  region  are  also 
cajiable  of  producing  variations  in  temperature,  and  it  is 
highly  probable  that  elevation  and  depression  have  re- 
sulted in  many  of  the  climatic  changes  of  which  there  is 
an  unwritten  record.^ 

Zones  of  Climate.— Zones  or  belts  whose  limits  are 
bounded  by  lines  of  equal  average  temperature  are  called 
isothermal  or  climatic  zones,  and  the  lines  bounding  thcin 
isothermal  lines  or  isotherms.  A  comparison  of  the  mai)  of 
the  astronomical  and  the  climatic  zones  shows  that  the 
correspondence  of  the  two  is  only  general.  The  former 
are  fixed  and  their  Ijoundary  lines  are  parallels  of  latitud.'. 
The  latter  change  their  positions  with  the  apparent  motion 
of  the  sun,  behaving  in  this  respect  like  the  /ones  of  winds 
and  calms.     In  fact  thev  are  all  governed  by  the  sani<'  law 


ISOTHERMS  FOR  JULY 


ISOTHERMS  FOR  JANUARY 


CLIMATE   AND   ITS  FACTORS  293 

and  arise  from  the  same  caiise — the  inclination  and  self- 
parallelism  of  the  earth's  axis. 

In  the  southern  hemisphere  the  isotherms  range  ap- 
proximately with  the  parallels.  What  may  be  inferred 
from  this  concerning  the  uniformity  of  temperature  with 
respect  to  latitude  ?  In  the  northern  hemisphere  the  iso- 
therms are  very  irregular.  In  which  direction  do  they 
bend  in  crossing  the  great  highlands  of  the  earth  ?  Explain 
the  cause  of  this.  In  the  North  Atlantic  warm  ocean  cur- 
rents and  their  drifts  cause  a  deviation  of  the  isotherms  ; 
explain  how  and  wli}-. 

By  what  isotherms  is  the  climatic  torrid  zone  limited 
north  and  south  ?  '"  Compare  the  position  in  Januar}'  and 
July.  In  the  spring  and  the  fall  its  position  corresponds 
roughly  with  that  of  the  astronomical  zone.  The  hottest 
areas  are  situated  not  on  the  equator,  however,  but  north 
of  it.  In  the  African  desert,  Arabia,  and  the  arid  lands  of 
the  United  States,  the  summer  temperature  is  above  38° 
(100°  F.)  and  during  unusual  hot  spells  it  sometimes 
reaches  49°  (120"  F.). 

The  isothermal  temperate  zones  are  limited  bv  the  lines 
of  21°  (70°  F.)  and  0'  (32°  F.).  The  summer  limit  of  the 
northern  zone  extends  high  into  the  arctic  regions.  The 
winter  limit  on  land  approximates  the  fortieth  parallel,  but 
on  the  ocean  it  is  much  higher.  In  the  Pacific  it  reaches 
to  the  sixtieth  parallel ;  in  the  Atlantic,  owing  to  the  drift 
of  the  Gulf  Stream  it  penetrates  the  polar  latitudes. 

Extremes  of  Climate.  —  The  isotherm  of  highest 
temperature  that  completely  girdles  the  earth  is  theoreti- 
cally the  thermal  equator.  Its  temperature  is  pr()l)ably 
between  27^  and  30^  (80^  to  80'^  F.).  There  are  several 
isolated  regions  having  a  considerably  higher  temperature, 
however.  An  extensive  region  in  the  Sahara  has  a  mean 
temperature  of  about  29°  (85°  F.),  and  in  Hindustan  and 


294 


PHYSICAL   GEOGEAPHY 


Africa  there  are  others  equally  warm.  lu  the  American 
continent  an  oval-shaped  region  extending  southward  from 
the  Gulf  of  California  has  about  the  same  mean. 

The  regions  of  extreme  cold  are  not  in  the  vicinity  of 
the  geographical  pole,  but  considerably  south  of  it.  In  the 
American  continent  the  area  of  extreme  cold  is  near  the 
Arctic  Archipelago.  In  Eurasia  it  is  a  little  to  the  east- 
ward of  the  Lena  River.  In  both  regions  the  mean  tem- 
perature is  not  higher  than— 17°  (0°  F.).  At  Werchojansk/ 
Siberia,  the  temperature  ranges  from  — 67°  (—90°  F.)  to 

32°  (90°  F.)  a  range 
of  one  hundred  and 
eighty  degrees — and 
probably  the  great- 
est on  the  earth. 

Changes  of  Sea- 
son. —  Because  the 
earth's  axis  is  in- 
clined to  the  plane 
of  its  orbit,  and  re- 
mains parallel  to  it- 
self while  the  earth 
revolves  around  the 
sun,  it  follows  that  the  rays  of  the  sun  do  not  fall  on  a 
given  place  always  at  the  same  angle. 

From  the  accompanying  diagrams  find  the  time  at 
which  the  sun's  rays  are  vertical  at  the  tropic  of  Cancer. 
What  is  the  season  at  this  time  in  the  northern  hemisphere  ? 
Are  the  sun's  rays  direct  or  slanting  in  the  southern  hemi- 
sphere? What  is  the  season  there  ?  What  are  the  seasons 
when  the  sun's  rays  are  vertical  at  the  equator?  On  a 
piece  of  thin  paper  trace,  with  a  pencil,  the  isothermal  hot 
zone  on  the  map  for  January,  p.  292 ;  cut  it  out  along  the 
lines,  and  place  it  in  its  proper  position  {i.e.,  for  January 


POSITION   OF   HEAT-RAYS   IN'JUNE 


CLIMATE   AND   ITS   FACTORS 


295 


ou  the  map  for  July).  The  parts  that  overlap  show  the 
region  where  summer  is  coutimious  all  the  year.  Compare 
this  result  with  the  diagram  ou  this  page.  What  parts  are 
not  covered  by  the 
heat -belt?  When 
the  heat-belt  is  far 
north  what  is  the 
season  in  the  North- 
em  Hemisphere  ? 
in  the  Southern  ? 
From  the  oscilla- 
tion of  the  heat- 
belt  show  how  five 
zones  of  tempera/ 
ture  result. 

The    inclination 
of  the  axis,  together  mth  its  parallelism,  as  the  earth  re- 
volves around  the  sun,  bring  the  temperate  zones,  in  turn, 


POSITION   OF   HEAT-RAYS   IN   DECEiMBER 


ANNUAL   MOVEMENT   OF   THE   HEAT-BELT 


to  a  position  where  the  sun's  rays  are  nearly  vertical.  It 
is  this  movement  that  causes  tin;  shifting  of  ilw.  zouos 
of  climate  alternately  north  and  south. 


296  PHYSICAL   GEOGRAPHY 

Tlie  alternation  of  the  four  seasons  is  realized  mainly  in 
the  temperate  zones.  In  the  greater  part  of  the  western 
coast  of  North  America  the  seasons  are  distinguished  more 
by  the  distribution  of  rain  than  by  variations  in  tempera- 
ture. Practically  there  are  two  seasons — a  rainy  and  a 
dry.  Within  the  greater  part  of  the  ton-id  zone  these  are 
also  about  the  only  distinctions  of  season.  In  the  frigid 
zones  the  distinctions  of  summer  and  winter  are  also  those 
of  day  and  night,  each  of  which  is  six  months  in  duration. 

Deserts. — There  are  many  extensive  areas  that  have 
little  or  no  rainfall.  If  the  rainfall  is  so  deficient  that 
irrigation  is  necessary  to  produce  crops  the  region  is  said 
to  be  arid ;  if  it  is  too  dry  for  food  crops,  it  is  generally 
considered  a  desert  region.  In  many  instances  there  is  no 
sharply  drawn  line  between  fertile  and  arid  lands,  or  be- 
tween arid  lands  and  deserts.  For  instance,  all  that  part 
of  the  Mississippi  basin  east  of  the  97th  meridian,  or  more 
strictly,  the  2,000-foot  contour — produces  an  abundance  of 
food  stuff.  West  of  this  contour,  however,  the  climate  be- 
comes much  drier,  and  beyond  the  lOOtli  meridian  or 
2,500-foot  contour,  crops  must  depend  mainl}^  on  irriga- 
tion. 

Farther  west,  turf  grass  is  replaced  by  scanty  bunch 
grass,  and  beyond  the  crest  of  the  eastern  ranges  of  the 
Rocky  Mountains  the  character  of  the  country  in  places 
approaches  that  of  a  typical  desert.  In  the  northern  part* 
of  the  Basin  Region,  the  cooler  climate  and  the  high 
ridges  wring  a  small  amount  of  water  from  the  clouds,  but. 
in  the  south  almost  all  vegetation  disappears  and  the  region 
is  absolutely  a  desert.  The  same  gradation  is  observed 
in  the  great  African  desert.  Both  north  and  south  of  the 
equatorial  rain-belt,  precipitation  decreases  little  by  little  ; 
fertile  lands  grade  imperceptibly  into  arid  belts,  and  the 
latter  into  deserts. 


CLIMATE   AND   ITS   FACTORS  297 

f  ~^^  the  South  American  deserts  the  line,  on  the  contrary, 
is  pretty  sharply  drawn,  and  the  same  is  true  of  the  North 
American  desert  and  the  Sahara,  if  they  are  approached 
from  the  western  side.  In  each  case  a  high  mountain- 
range  forms  a  barrier  to  the  rain  winds,  sharply  dividing 
a  fertile  area  from  a  desert. 

Only  a  small  part  of  the  extensive  desert  areas  is  desti- 
tute of  vegetation,  and  in  such  parts  the  finely  pulverized 
rock  waste,  or  "sand"'  shifts  hither  and  thither  with  the 
winds.  It  is  in  such  regions  that  the  fierce  simoon  and  sim- 
ilar sand-storms  prevail.  The  Colorado  Desert,  in  south- 
eastern Califoi-nia,  is  an  excellent  example  of  the  kind. 

The  climate  of  desert  regions  is  marked  bv  peculiarities 
and  extremes.  The  winds  are  hot  sand-blasts  and  whirls  ; 
the  scanty  rains  come  usually  in  the  form  of  cloud-bursts ; 
the  temperature  is  one  of  frightful  extremes ;  the  relative 
humidity  of  the  atmosphere  rarely  exceeds  thirty  per  cent, 
of  saturation.  Notwithstanding  all  this,  desert  climate  is 
wonderfully  healthful. 

Any  fertile  spot  in  a  desert  is  called  an  oasis,  and  the 
latter  is  fertile  because  it  is  more  or  less  abuudautly  sup- 
plied with  water.  On  account  of  the  presence  of  water, 
the  oasis  commonly  yields  a  goodly  supply  of  footl-stufls. 
Various  causes  contribute  to  the  formation  of  oases.  The 
underlying  strata  may  be  impervious  to  water,  thereby 
preventing  the  latter  from  sinking  deep  into  the  soil, 
or  there  may  be  a  mountain-crest  that  is  sufficiently  liigh 
to  condense  and  precipitate  more  or  less  nujisturc.  Tlie 
water  flowing  down  the  slopes  percolates  througli  the  fine 
rock  waste  at  the  l)ottom,  much  of  it  being  held  there  in 
suspension.  The  oases  of  the  North  American  deserts  are 
of  this  character. 

The  distribution  of  deserts  constitutes  an  interesting 
study.     There  are  practically  two  zones,  situated  mainly 


398  PHYSICAL   GEOGRAPHY 

between  the  20tli  and  SOtli  parallels,  north  and  south,  that 
contain  nearly  all  the  desert  and  arid  lands  of  the  earth.  In 
Eurasia  and  Africa  a  belt  of  desert  stretches  from  the  west- 
ern coast  almost  through  the  continent.*^  In  North  America 
this  belt  is  nearly  1,000  miles  east  and  west.  The  deserts 
of  the  Southern  Hemisphere  are  smaller  in  area  only  be- 
cause of  the  smaller  laud  area.  In  South  America  it  lies 
at  the  eastern  base  of  the  Andes  ;  in  Africa,  south  of  the 
Kongo  water-shed;  in  Australia,  it  extends  almost  across 
the  continent. 

Various  causes  contribute  to  make  arid  and  desert  con- 
ditions ;  but  in  any  case  a  desert  is  a  desert,  not  because 
of  any  natural  sterility  of  the  soil,  but  because  of  the  lack 
of  moisture.  '•*  In  some  localities  a  high  mountain -range 
that  faces  the  sea-winds  condenses  all  the  moisture  they  con- 
tain and  the  opposite  slope  with  its  outlying  area  is  there- 
fore a  desert.  Explain  why  the  Peruvian  desert  of  South 
America  is  west  of  the  Andes,  and  the  desert  of  Argentina 
lies  to  the  east  of  these  ranges.  Why  is  the  region  east 
of  the  Cascade  and  Sierra  Nevada  Kanges  either  arid  or 
desert  ?  What  effects  have  the  Himalaya  Mountains  on 
the  rainfall  of  the  region  to  the  northward  ? 

In  other  instances  the  desert  conditions  arise  from  other 
and  more  complex  causes.  Thus,  between  the  20th  and 
30th  parallels  there  is  a  downward  movement  of  atmos- 
pheric currents  ;  explain  why  these  may  produce  deficiency 
or  absence  of  rainfall  (p.  288).  In  some  localities  the 
winds  blowing  inland  from  the  sea  may  enter  localities 
having  a  temperature  higher  than  that  of  the  winds  them- 
selves, and  in  such  instances  their  moisture  is  not  con- 
densed. The  Australian  and  African  deserts  result  mainly 
from  one  or  the  other,  or  both,  of  these  causes.  They  are 
unfortunately  situated  with  reference  to  latitude,  and  they 
also  are  lacking  in  high  mountain-ranges. 


CLIMATE   AND   ITS   FACTORS  299 

QUESTIONS  AND  EXERCISES.— Referring  to  any  good  map,  de- 
termine the  climate  of  South  America  from  the  following  suggestions 
giving  a  reason  for  each  statement :  What  are  the  conditions  of  tem- 
perature of  the  northern  part  ?  How  do  those  of  the  southern  part 
differ  ?  In  which  part  is  temperature  the  basis  of  the  seasons  ?  In 
which  is  rainfall?  From  which  direction  do  the  rains  of  the  northern 
part  come  ?  of  the  southern  part  ?  What  is  the  effect  of  the  Andes 
Mountains  on  the  distribution  of  the  rainfall  ?  Give  the  location  of 
the  desert  and  arid  regions.  Note  the  effects  of  altitude  on  the  climate 
of  the  highlands  ;  of  the  lowlands.  What  evidence  does  the  map  give 
to  show  whether  the  rainfall  of  the  Amazon  basin  is  profuse  or  deficient  ? 
Explain  why  the  basin  of  the  Orinoco  has  two  rainy  and  two  dry 
seasons. 

Compare  the  Asian  and  American  deserts  as  to  origin.  How  do  the 
African  deserts  compare  in  this  respect  ? 

Prepare  a  summary  of  the  climatic  conditions  of  the  state  or  county 
in  which  you  live,  noting  especially  any  facts  not  ordinarily  included 
in  the  general  outlines  of  the  subject.  From  the  United  States  Weather 
Bureau  obtain  the  following  :  highest  temperature  observed,  lowest 
temperature  observed,  mean  for  each  month,  mean  annual  rainfall, 
mean  for  each  month,  number  of  rainy  days  for  any  year,  general 
direction  of  the  winds,  other  relevant  facts. 


COLLATERAL  READING  AND  REFERENCE. 

Davis. — Elements  of  Meteorology. 
Waldo.  — Elementary  Meteorology. 
Greely. — American  Weather. 


NOTES 

'  To  these  may  be  added  the  eflfect  of  ocean  currents.  It  is 
sometimes  stated  that  the  warintli  of  western  Kur<)|M' — the  Brit- 
ish Isles,  especially— is  due  to  the  (fulf  Stream,  and  that  of  tlm 
western  United  States  to  the  infhience  of  the  Japan  (Current. 
So  far  as  their  temperature  in  general  is  concerned,  such  a  state- 
ment is  untenable.  Ocean  currents  accomplish  very  potent  re- 
sults, however,  but  not  because  of  their  efTects  on  climat<>. 
Thus,  the  warm  drift  of  the  (iulf  iStream  is  carried  by  tlie  I'n-- 
vailing  Westerlies   into   about   every   bay  and  cove   of    western 


300  PHYSICAL   GEOGRAPHY 

Europe;  and  as  a  result  the  harbors  —  even  as  far  north  as 
Hainmerfest — are  free  from  ice  all  the  year. 

"  A  noticeable  and  highly  impoi-tant  difference  between  a  mari- 
time and  a  continental  climate,  is  the  daily  range  of  tempera- 
ture. In  a  maritime  climate  this  rarely  exceeds  twenty  degrees 
(F. ),  while  in  a  few  inland  regions  the  fluctuations  may  be  twice 
as  great. 

^  That  is,  if  the  axis  of  the  earth  were  to  incline  forty  degrees, 
tlien  the  polar  and  the  tropical  circles  would  have  a  correspond- 
ing distance  from  the  poles  and  from  the  equator,  and  the  tem- 
perate zones  each  would  be  ten  degrees  in  width,  instead  of 
forty-three.  Or,  if  the  longitude  of  perihelion  were  to  change 
materially,  the  winters  of  the  northern  hemisphere  might  be 
longer  by  several  days  than  the  summers,  thus  causing  the  ice 
and  snow  to  collect  faster  than  it  would  melt,  thei-eby  in  time 
causing  far-reaching  changes. 

'  The  elevation  of  a  region  is  thought  to  result  in  a  lowering  of 
its  mean  temperature,  and  the  depression  of  its  surface,  it  is  be- 
lieved, has  an  opposite  effect.  The  surface  of  New  York  and  the 
New  England  States  was  about  1,000  feet  higher  during  the 
Glacial  Epoch  than  at  present. 

^  The  mean  annual  temperature  of  a  region  reveals  but  little 
concerning  its  actual  conditions  of  temperature.  These  can 
be  studied  only  from  monthly  isotherms— that  is,  by  comparing 
the  monthly  range  of  temperature  and  climate.  For  this  reason, 
instead  of  a  chart  of  annual  isotherms,  it  has  been  deemed  wiser 
to  prepare  two  charts,  one  showing  the  isotherms  for  January, 
the  other  for  July. 

"Werchojansk  (or  Verkoyansk)  is  four  hundred  miles  north  of 
Yakutsk,  Siberia.  The  two  are  in  probably  the  coldest  inhab- 
ited region  in  the  world.  The  highest  temperature  taken  under 
standard  conditions — that  is,  shaded  by  a  double  roof  with  an 
air-space  between,  and  exposed  at  a  distance  from  any  radiating 
surface — seems  to  have  been  recorded  at  Warglar,  Algeria,  where 
the  mercury  marked  127°  F.  In  the  Colorado  Desert  an  unoffi- 
cial temperature  of  136°  has  been  noted.  In  this  case,  however, 
it  is  doubtful  if  a  properly  exposed  thermometer  would  have 
registered  so  much  by  ten  or  fifteen  degrees.  No  temperature 
in  this  region  recorded  by  the  Weather  Bureau  has  exceeded  122°, 
though  there  are  several  localities,   such   as  Sal  ton  Lake  and 


CLIMATE   AND   ITS   FACTORS  301 

Death  Valley,  where  the  temperature  ranges  higher  than  at  any 
of  the  Weather  Bureau  stations.  The  author  has  repeatedly 
noted  temperatures  in  the  Colorado  Desert  varying  from  130°  to 
145°  registered  by  a  thermometer  exposed  to  the  direct  rays  of  the 
sun.  The  experience  of  General  Greely,  U.S.A.,  Chief  Signal 
Officer,  shows  the  range  of  human  endurance.  At  Fort  Conger, 
Lady  Franklin  Bay,  he  and  his  party  experienced  no  intolerable 
discomforts  with  the  temperature  as  low  as  —  66°,  the  same  officer 
served  in  Arizona  where  the  shade  temperature  was  119°  and  that 
of  an  unprotected  thermometer  144°. 

'  The  shifting  soil  of  deserts  is  popularly  regarded  as  sand.  As 
a  matter  of  fact  it  consists  of  about  every  kind  of  rock  Avaste 
broken  and  pulverized  by  the  impact  it  receives  as  it  is  blown 
aljout  by  the  wind.  Doubtless  it  contains  more  or  less  quartz, 
but  in  general,  true  quartz  sand  is  rare.  In  the  Colorado  antl 
Mojave  Deserts  the  detritus  passing  for  sand  is  broken  felspathic 
rock  ;  in  certain  localities  of  the  Arabian  Desert  it  is  a  red.  loamy 
soil. 

^  "The  districts  of  the  Sahara  destitute  of  oases  present  a  f(  )niii(l  - 
able  aspect.  The  path  which  the  feet  of  the  camels  have  marked 
out  in  the  immense  solitude  points  in  a  straight  line  toAvard  the 
spot  which  the  caravan  wishes  to  reach.  Sometimes  these  faint 
footmarks  are  covered  with  wind-blown  rock  waste,  and  the 
travellers  are  obliged  to  consult  the  compass,  the  horizon,  a  dis- 
tant sand-hill,  a  bush,  a  heap  of  ciimels'  bones,  or  some  other 
indications  which  the  practised  eye  of  the  Tuareg  alone  can  un- 
derstand as  the  means  by  which  the  road  is  recognized.  Vege- 
tation is  rare,  and  the  only  plants  to  be  seen  are  the  scrulj,  con- 
sisting mainly  of  thorny  Mimosas  ;  in  some  sandy  deserts  tin 're  is 
a  complete  absence  of  all  kinds  of  vegetation.  The  only  animals 
to  be  found  are  scorpions,  lizards,  vipers,  and  ants.  During  the 
first  few  days  of  the  Journey  a  few  indefatigable  iiuiividuals  of  the 
lly  tribe  accompany  the  caravan,  but  they  are  soon  killed  by  the 
lieat;  even  the  flea  itself  will  not  venture  into  tliese  dreadful 
region.s.  The  intense  radiation  of  tln^  enoniious  wliitc  or  ml 
surface  of  the  desert  dazzles  the  eyes;  in  tiiis  iiliii.liiiu'  light 
every  object  appears  to  be  clothed  with  a  s..iiil)rr  and  prrtfr- 
natural  tint.  Occasionally  the  traAcllcr,  when  sitting  upon  his 
camel,  is  seized  with  a  kind  of  brain  fever,  which  causes  him  to 
see   the   most  fantastical   objects    in    his  delirium.      Mven  those 


I 


302  PHYSICAL   GEOGRAPHY 

who  retain  the  entire  possession  of  their  faculties  and  clearness 
of  vision  are  beset  by  distant  mirages ;  palm-trees,  groups  of 
tents,  shady  mountains  and  sparkling  cascades  seem  to  dance 
before  their  eyes  in  misty  vapor.  When  the  wind  blows  hard, 
the  traveller's  body  is  beaten  by  grains  of  sand  which  penetrate 
even  through  his  clothes  and  prick  like  needles.  Stagnant  pools 
or  wells,  dug  with  great  labor  in  some  hollow  or  other,  from  the 
sides  of  which  oozes  out  a  brackish  moisture,  point  out  each 
day  the  end  of  the  stage.  But  often  this  unwholesome  swamp, 
where  they  hoped  to  recruit  their  energies,  is  not  to  be  found, 
and  the  people  of  the  caravan  must  content  themselves  with  the 
tainted  water  with  which  they  filled  thair  flasks  at  the  preceding 
stage.  It  is  said  that  in  times  of  great  need  travellers  have  been 
compelled  to  kill  their  dromedaries  in  order  to  quench  their 
thirst  in  the  nauseous  liquid  contained  in  the  stomachs  of  these 
animals. ' ' — Elisee  Reclus. 

°  In  popular  literature  the  climate  of  deserts  is  supposed  to 
have  baneful  properties,  and  the  expression  "  poisonous  emana- 
tions ' '  has  a  prominent  place  in  many  newspaper  accounts.  As 
a  matter  of  fact,  desert  air  is  unsurpassed  so  far  as  salubrity  is 
concerned.  It  is  so  free  from  the  germs  that  produce  or  hasten  dis- 
ease, that  meat  will  not  putrefy  and  food  will  not  ferment.  Sep- 
ticaemia, or  "blood-poisoning,"  rarely  if  ever  follows  accidental 
wounds  or  surgical  operations,  and  tuberculosis  originating  in 
such  localities  is  unknown. 


CHAPTER   XYII 

THE  DISPERSAL  OF  LIFE 

There  are  two  lessons  iu  nature  tliat  probably  every 
human  being  of  mature  years  lias  learned,  namely— that 
the  earth  is  full  of  organisms  endowed  with  that  niys- 
terious  force  called  life,  and  that  the  life-forms  are 
grouped  in  kinds  or  species.  Moreover,  while  the  indi- 
viduals of  a  species  closely  resemble  one  another,  those 
of  different  species  are  commonly  very  unlike. 

Almost  ever}'  living  bod}^  or  organism  passes  througli 
several  stages  or  conditions.'  It  first  appears  in  the  form 
of  a  germ  enclosed  in  an  envelope  called  an  egg,  or  per- 
haps, a  seed.  Under  the  action  of  heat,  or  moisture,  or 
both  heat  and  moisture,  the  egg  or  seed  passes  througli 
various  stages  of  development  in  which  it  gradually  ap- 
proaches its  mature  form — the  condition  that  immediately 
precedes  death.  In  general,  the  egg  develops  into  a  life- 
form,  known  as  an  animal,  the  seed  into  a  plant.  The  egg 
may  contain  both  food  and  moisture  as  well  wdthin  its  en- 
velope ;  but  the  seed  contains  food  only.  The  egg  very 
easily  loses  its  vitality  or  life  principle  ;  the  seed  may  ic- 
tain  its  vitality  for  months,  or  even  years.  The  oirsi)iiiig 
of  the  egg  almost  always  possesses  the  power  of  moving 
from  place  to  place  in  one  or  another  of  its  forms  of  life ; 
the  offspring  of  the  seed,  on  the  contrary,  cannot  move  ; 
it  spends  its  lif(!  in  the  spot  in  whicli  it  devcloixMl  into  life. 

The  seed-form  of  the  organism  is  remarkably  adaj^tcd 
for   transportation    and  dispersal.     Commonly   the    seeds 

303 


304 


PHYSICAL  GEOGRAPHY 


are  strong  enough  to  resist  not  a  little  mechanical  force. 
Those  of  some  species  will  endure  a  temperature  but  little 
lower  than  that  of  boiling  water ;  they  will  likewise  endure 
the  severest  cold,  and  almost  ahvays  they  are  enclosed  in  a 
water-tight  case.  The  egg,  on  the  other  hand,  will  not 
endure  extremes  of  temperature,  nor  will  it  survive  the 
slightest  injury.     As  a  rule,  both  seeds  and  eggs  float  on 


A  BARRIER   THAT  CERTAIN   SPECIES  CANNOT  PASS 

water,  and  many  kinds  are  so  light  that  they  are  carried 
for  miles  in  the  air. 

The  stage  of  growth  and  development  is  a  condition  of 
the  greatest  danger  to  the  existence  of  the  organism. 
During  this  period  it  quickly  and  easily  succumbs  to  the 
most  trifling  changes  in  its  surroundings.  At  this  time, 
too,  it  is  apt  to  be  the  prey  of  higher  organisms  that  kill 


THE   DISPERSAL   OF   LIFE  305 

and  devour  it.  ludeed,  so  great  is  the  mortality  during 
the  period  of  development  that,  in  many  species,  not  more 
than  one  or  two  individuals  in  many  thousand  reach  the 
state  of  maturity.^ 

The  mature  stage  of  the  organism  follows  that  of  de- 
velopment. In  this  condition  it  has  but  one  objective 
toward  which  all  its  energies  tend,  namely — the  reproduc- 
tion of  its  kind.  This  accomplished,  sooner  or  later  it  dies  ; 
that  is,  the  vital  principle  leaves  it,  and  it  is  quickly  resolved 
into  the  mineral  elements — the  "  dust  " — which  gave  it  ex- 
ternal form  and  structure.  Not  a  few  species  have  special 
means  for  the  protection  of  their  bodies,  and  nearly  all 
possess  special  organs  for  the  purj)ose  of  nutrition,  and 
the  higher  species  have  organs  of  locomotion. 

Laws  of  Structure. — Many  laws  are  concerned  in  the 
growth,  development,  and  reproduction  of  organic  forms, 
but  there  are  three  that  govern,  directly  or  indii-ectly,  every 
form  of  life.     These  are  heredity,  nutrition,  and  variation. 

The  law  by  virtue  of  which  the  germs  of  organisms  de- 
velop and  mature,  each  into  a  form  of  its  own  kind,  is 
called  heredity.  The  germ  of  a  species  always  reproduces 
forms  like  those  of  the  parents  or  ancestors.  Acorns  always 
produce  oak-trees,  animals  beget  each  of  its  own  kind,  and 
the  germ  that  in  the  human  system  produces  disease,  breeds 
notliiug  but  disease  of  its  own  kind. ' 

A  seed  or  an  egg  develops  into  an  organism  that  be- 
comes an  ancestor  of  many  thousand  generations,  aggi'e- 
gating  millions  of  individuals.  But  in  obedience  to  the 
law  of  heredity,  the  individuals  of  tlir  last  generation  will 
not  very  greatly  differ  from  their  ancestor,  nor  will  tiny 
differ  from  one  another. 

The  process  by  which  food,  once  wiiliiii  the  body  of  an 
organism,  is  decomposed  and  then  made  a  part  of  the 
structure  of  the  organism  is  called  nutrition,  or  feeding. 


306 


PHYSICAL   GEOGKAPHY 


In  obedience  to  this  law,  new  tissue,  that  is,  flesh,  blood, 
bones,  etc.,  is  constantly  being  made,  and  older  tissue,  no 
longer  useful,  is  cast  off  and  destroyed.  The  number  of 
substances  required  in  nutrition  is  few.  Nearly  three- 
quarters  of  the  weight  of  ever}'  organic  being  consists  of 
water ;  in  many  instances  97  per  cent,  is 
water.  The  remaining  j)art  is  composed 
mainly  of  compounds  of  carbon,  nitrogen, 
hydrogen,  and  phosphorus.  The  food 
must  contain  all  these  substances  or  the 
organism  will  not  mature.  As  a  rule, 
plants  obtain  their  food  from  the  min- 
kingdom,  and  animals,  either 
rectly  or  indirectly,  from  plants. 
Variation  is  the  law  in  obedi- 
ence to  which  organisms  are 
changed,  or  change  themselves, 
to  meet  the  conditions 
necessary  to  their  exist- 
ence. Thus,  under  cul- 
tivation, the  wild  rose, 
no  longer  needing  its 
multitude  of  stamens, 
develops  them  into  pet- 
als.     Under   the   condi- 

VARIATION:    ADAPTED   TO   ITS   ENVIRON-     tioUS     impOSed     by    itS 

'^^'^'^  environment,  the  almond 

has  varied  its  development  by  taking  the'form  of  the  peach 
and  the  nectarine. 

Birds  that  for  long-continued  generations  have  obtained 
their  food  from  the  Avater  have  become  either  swimmers  or 
waders,  and  many  species  of  those  that  scratch  the  ground 
to  obtain  food  have  gradually  lost  the  power  of  extended 
flight.    The  great  diversity  observable  in  the  various  mem- 


THE   DISPEESAL   OF   LIFE  307 

bers  of  the  dog  family  is  a  familiar  example  of  the  effects 
of  variation.  The  horse  of  present  times  has  but  one  toe, 
but  the  ancestors  of  the  species  in  Miocene  times  had 
three,  and  in  Eocene  times  four  toes  on  the  fore  feet.^ 
The  birds  of  early  geological  periods  were  much  more  rep- 
tilian in  character  than  those  of  present  times.  Some  of 
the  reptiles,  too,  have  lost  their  feet  and  are  scarcely  a 
remove  from  serpents. 

Environment. — Variation  of  species  is  the  result  of 
food,  temperature,  and  moisture.  These  are  the  conditions 
with  which  every  organism  has  to  battle  for  existence, 
and  these  determine  all  its  habits.  If  the  environment  of  a 
species  changes,  one  of  three  things  is  pretty  certain  to 
take  place  :  the  species  dies,  it  migrates,  or  else  it  survives 
with  changed  habits. 

Thus,  if  in  a  given  locality,  the  rainfall  lessens  materially, 
the  turf  grass  quickly  discovers  it.  In  order  to  obtain  the 
necessary  moisture,  an  enormous  development  of  rootlets 
takes  place,  and  if  this  development  does  not  procure  tlie 
necessary  amount  of  water,  the  turf  grass  gradually  dis- 
appears. If  a  certain  species  requires  an  aggregate  of  tt'U 
inches  of  rain,  distributed  monthly,  it  will  perish  if  the 
rainfall  decreases  to  nine  inches,  or  if  there  is  a  drought 
of  more  than  thirty  consecutive  days.  It  will  thriven  and 
possibly  extend  its  limits  if  the  annual  precipitation  in- 
creases to  twelve  inches. 

The  fruit  of  the  common  gooseberry,  cultivated  in  moist 
regions,  has  a  smooth  surface;  but  transplanted  t(;  ariil 
regions  and  left  to  grow  wild,  the  berry  finally  matures, 
covered  with  leathery  spines.  Cultivation,  wliicli  is  only 
another  name  for  change  of  environment,  has  resulted  in 
all  the  beautiful  varieties  of  roses;  it  lias  ]>roduced  the 
domesticated  fruits  from  wild  fruits  ;  it  lias  niatlc  the  dif- 
ference between  the  wild  fowl  and  the  domestic  fowl  of 


308  PHYSICAL  GEOGRAPHY 

the  same  species.  Since  the  territory  inhabited  by  a 
species  is  either  enlarged  or  decreased  by  a  change  in 
food,  temperature,  and  moisture,  and  since  a  change  in 
any  of  these  factors  sooner  or  later  results  in  variation,  it 
is  evident  that  the  distribution  and  variation  of  species  is 
governed  mainly  by  geographic  laws. 

Causes  that  apparently  are  the  most  trivial  are  not  in- 
frequently attended  by  far-reaching  consequences.  For 
example,  the  mongoose  was  introduced  into  Jamaica  in 
order  to  exterminate  the  cane-rat,  then  a  menace  to  the 
sugar-planter.  The  mongoose  did  not  lessen  the  number 
of  cane-rats,  but  it  exterminated  one  or  two  species  of 
ground-bird,  and  with  their  disappearance  there  came 
such  sAvarms  of  "cattle-ticks"  and  "grass-lice"  that  the 
existence  of  cattle-raising  was  threatened.  The  ground- 
birds  had  prevented  any  great  increase  of  the  insect 
species ;  but  when  the  former  were  killed,  the  latter  be- 
came an  intolerable  pest. 

Animals  and  Plants. — Plants  are  lower  in  the  scale 
of  life  than  animals.  A  few  species  excepted,  they  have 
not  the  power  of  voluntary  motion,  and  if  they  possess 
the  power  of  sensation  at  all,  the  latter  is  of  the  very 
feeblest  degree.  They  derive  their  nutrition  mainly  from 
the  ground  and  the  air,  being  able  to  transform  mineral 
matter,  such  as  water,  lime,  potash,  carbon,  etc.,  into  plant 
tissue.  With  one  or  two  exceptions,  plants  inhale  carbon 
dioxide  and  exhale  oxygen. 

Plants  exhibit  only  in  the  feeblest  degree,  if  at  all,  the 
faculty  of  intelligence,  and  this  is  observed  only  in  the 
way  they  seek  their  food.  The  roots  of  a  plant  will  grow 
in  the  direction  of  water,  and  the  flower  will  open  with 
the  light  and  close  in  the  presence  of  darkness.  No  spe- 
cies is  known  that  will  pursue  its  prey  or  flee  from  an 
enemy.     And  the  reason  is  obvious :  the  plant  does  not 


THE   DISPERSAL   OF   LIFE  309 

exist  at  the  expense  of  other  life-forms ;  it  merely  trans- 
forms dead  mineral  matter  into  living  matter,  which  is  to 
become  the  food  of  higher  forms.  Nevertheless,  the  jilaut 
contains  a  vital  force  that  causes  it  to  live,  grow,  develop, 
and  reproduce ;  and  when  this  vital  force  is  spent,  the 
plant  dies. 

Animals — even  the  lowest  species — are  far  more  com- 
plex in  organization  than  plants.  The  animal  lives  by  the 
destruction  of  other  forms  of  life,  and  therefore,  in  general, 
it  must  possess  the  powers  of  locomotion,  prehension,  or 
grasping,  and  also  some  means  of  defence.  All  animals 
possess  intelligence,  and  some  of  the  higher  forms  have  the 
faculty  of  reason.  No  exact  line  of  division,  however, 
can  be  drawn  between  animals  and  plants. 

Dispersal  of  Life. — The  distribution  of  life  over  the 
globe  is  not  a  matter  of  chance  ;  on  the  contrary,  it  exhibits 
a  character  that  can  result  only  by  the  operation  of  fixed 
laws.  Moreover  it  must  be  examined  from  two  sides, 
namely  —  the  means  possessed  by  animals  and  plants 
to  disperse  and,  conversely,  the  barriers  that  operate  to 
prevent  dispersal. 

The  means  of  dispersal  are  many.  All  the  higher  species 
of  animals  possess  the  power  of  voluntary  motion.  Quad- 
rupeds use  their  feet ;  birds  fly  ;  nearly  all  insects  have 
at  least  one  stage  of  develo])ment  in  which  tlicy  ])ossess 
wings ;  and  fishes  swim.  Marine  currents  carry  niajiy 
species  from  the  place  of  their  birth  to  distant  parts  ;  and 
still  other  s])ecies  are  carried  l)y  floating  matter,  and  in 
the  cro])  of  birds. 

Seeds  of  plants  are  carried  by  the  winds,  by  running 
waters,  and  in  the  crops  of  birds  or  in  the  digestive  ai)pa- 
ratus  of  animals.  Commerce  is  responsible  for  tlic  dis- 
persal of  most  species  Tised  for  food  anil  many  that  arc 
baneful  to  humanity.''     In  short,  abnost   every   organism 


310  PHYSICAL   GEOGKAPHY 

possesses  means  that,  under  ordinaiy  circumstances  would 
give  it  a  far  wider  territory  than  it  now  possesses. 

The  natural  or  unrestricted  migi'ation  of  species  presents 
an  interesting  aspect.  In  the  temperate  zones,  as  a  rule, 
the  dispersal  has  been  from  west  to  east ;  in  the  torrid 
zone  it  has  generally  been  in  the  opposite  direction.  A 
moment's  thought  will  suffice  to  show  the  reason  for  this 
law,  namely — the  direction  of  atmospheric  and  marine 
currents. 

But  there  are  many  regions  swept  by  marine  currents  in 
which  the  species  they  carry  will  not  thrive,  and  quite  as 
many  traversed  by  winds  that  the  winds  never  sow  with 
seeds,  and  the  soil  never  fertilizes.  Such  extraordinary 
effects  cannot  exist  Avithout  causes,  and  these  are  the 
natural  barriers  to  distribution. 

Barriers. — The  barriers  to  dispersal  are  even  more 
j^otent  than  its  agents.  These  may  be  reduced  to  two 
classes — physiographic  bm-riers  and  environment.  Chief 
among  the  former  are  the  high  mountain-ranges,  oceans 
and  deserts. 

High  mountain-ranges  form  a  tolerably  effective  barrier 
to  species  not  provided  with  means  of  locomotion,  and  the 
more  extensive  the  highland  the  gi-eater  the  difference  of 
the  species  on  the  opposite  sides.  There  are  tAvo  reasons 
for  this.  In  the  first  place,  if  the  species  are  unprovided 
with  means  for  migration  they  cannot  cross  it ;  in  the 
second  place,  the  conditions  of  climate  on  the  opposite 
sides  of  high  mountains  are  so  different  that  the  species 
might  not  survive,  even  if  transported.  The  low  temper- 
ature of  the  summit  of  the  range  might  also  be  fatal. 

The  ocean  and  other  wide  expanses  of  Avater  are  effective 
barriers  to  land  plants  and  animals.  A  few  birds  endowed 
Avdtli  unusual  powers  of  flight,  have  crossed  the  ocean  ; 
seeds  and  eggs  have  also  made  the  passage  ;  and  not  a  few 


THE   DISPEESAL   OF   LIFE 


311 


species  have  been  transported  in  vessels.  But  all  these 
are  accideutal  migrations,  and  even  then  the  question  of 
environment  would  still  remain  to  be  determined. 

Deserts  present  the  same  difficulties.  Few  species  are 
able  to  cross  them  ;  fewer  still  to  remain  in  them,  and  the 
barrier  once  surmounted,  there  ma}'  be  changed  conditions 
which  still  forbid  the  intrusion  of  the  species. 

Environment  has  been  considered  in  the  light  of  a 
cause  of  variation,  but  it  is  far  more  potent  as  a  barrier  to 


A   DESERT    BARRIER 


the  existence  of  a  species.  If  a  species  requires  a  tempera- 
ture not  lower  than  0°  (32°  F.),  it  will  perish  in  a  dimat.' 
having  a  lower  range.  If  it  requires  an  annual  rainf.-.U  ..f 
thirty  inches,  it  will  perish  if  tl.e  prccipit.-itioii  f.-ills  1.. 
twenty-nine  inches;  or  if  it  recpiiresa  monthly  distribution 
of  rain,  it  will  net  survive  any  c.nsi.lrrablr  numbrr  ..f 
droughts  of  more  than  thirty  days. 


313 


PHYSICAL   GEOGRAPHY 


Thus  it  is  seen  that  every  species  demauds  certain  con- 
ditions of  food,  temperature,  and  moisture.  If  these  be  of 
\vide  range  the  species  will  inhabit  a  wide  geographical 
territory  ;  if  they  be  narrow  in  range,  the  limits  of  its  ex- 
istence will  be  correspondingly  narrow.  If  the  proportion, 
or  degree,  or  quality  change,  even  minutely,  the  species 
will  vary ;  if  they  vary  materially  the  species  will  perish. 


THERE   MAY   BE  ENEMIES   THAT   OPPOSE  THE  NEW-COMER 


It  sometimes  occurs,  however,  that  a  species,  once  in- 
troduced and  acclimated,  is  unable  to  maintain  itself,  or 
maintaining  itself,  is  unable  to  spread  to  any  extent  over 
a  region  whose  soil  and  climate  are  in  every  way  adapta- 
ble. There  are  several  reasons  for  this.  The  region 
may  have  been  already  pre-empted  by  other  species  that 
resist  encroachment,  or  there  may  be  enemies  constantly 
at  work  seeking  to  exterminate  the  new-comer.      As  a  re- 


THE   DISPERSAL    OF   LIFE  313 

suit,  there  are  some  species  capable  of  general  dispersion 
that  are  confined  to  narrow  limits,  while  others  have  spread 
themselves  broadcast  over  both  continents. 

Thus,  turf -grass  is  easily  cultivated,  but  it  has  so  many 
enemies  that  in  a  few  localities  only  does  it  thrive  in  a 
wild  state.  The  willow,  on  the  contrary,  spreads  wherever 
it  is  introduced.  The  ostrich  does  not  extend  its  territory, 
but  the  rabbit  has  become  a  pest  in  almost  ever}-  part  of 
the  civilized  world. 

QUESTIONS  AND  EXERCISES.— Study  the  common  thistle,  the 
dandelion,  or  the  winged  maple,  and  show  how  these  species  may  be 
spread. 

In  the  temperate  regions  of  North  America  in  what  general  direction 
will  those  species  depending  on  the  winds  for  distribution  be  most 
apt  to  spread  ? 

Note  any  instance  that  has  come  under  your  personal  observation  in 
which  plants  have  been  carried  into  new  territory  by  winds,  by  running 
streams,  or  by  waves. 

Note  any  instance  within  your  knowledge  in  which  either  a  natural 
feature  or  the  activity  of  man  has  formed  a  barrier  to  the  dispersion  of  a 
plant  or  an  animal  species. 

What  advantages  have  each  of  the  following  species  for  dispersal  ? 
the  camel,  man,  the  burdock,  the  ant,  the  snake,  the  cotton  plant. 

The  sting  of  the  tsetse  fly,  an  insect  of  Africa,  is  fatal  to  most  cattle, 
but  the  offspring  of  those  that  survive,  are  immune  from  its  attacks  ; 
how  will  this  fact  affect  the  dispersal  of  cattle  ? 

COLLATERAL  READING  AND  REFERENCE 

Shalkr. — Nature  and  IMan  in  North  America. 
Rebway.— The  Arid  Kei,don  of  the  United  States. 


NOTES 

'  Thus,  aiiiong  plants,  these  staf,'es  are  the  seed,  tlie  sproiitini? 
plant,  and  the  mature,  llowerin},'  stafjre.  In  animals  tliey  are  tlie 
egg,  the  embryo,  and  the  adult  individual.  Among  the  lower 
forms  of   life   the   changes  are   often    far   more   complex.      Most 


314  PHYSICAL   GEOGRAPHY 

insects  pass  through  the  forms  of  egg,  larva,  pupa,  and  imago, 
and  in  some  species  tliere  are  still  other  intermediate  forms. 

"^  As  the  enemies  to  a  species  increase,  its  fecundity  is  apt  also 
to  increase.  Thus,  the  spawn  of  a  female  cod-fish  aggregates  sev- 
eral million  eggs.  If  all  these  were  to  hatch  and  mature,  the  sea 
would  hold  but  a  few  generations. 

*  Since  the  discovery  of  the  fact  that  many  diseases  are  due  to 
the  growth  and  development  of  minute  organisms  within  the 
human  body,  the  science  of  surgery  and  that  of  sanitation  have 
been  greatly  aided.  Septicemia,  variously  known  as  "hospital 
fever"  and  "blood-poisoning,"  once  the  bane  of  every  hospital, 
are  now  comparatively  rare,  and  such  diseases  as  small-pox, 
typhoid  fever,  and  cholera  may  be  readily  quarantined  and 
stamped  out. 

*  Because  of  this  struggle,  that  has  been  waging  ever  since  life 
first  appeared  on  the  earth,  only  the  individuals  that  can  best 
adapt  themselves  to  circumstances  are  able  to  survive.  Varia- 
tion is  not  always  a  gradual  change  in  a  whole  species  ;  it  is 
quite  as  often  a  distinctive  change  in  several  individuals,  and  the 
transmitted  change  that  marks  the  descendants. 

'  The  Norwegian  rat  in  America,  the  Colorado  potato-beetle  in 
Europe,  and  the  English  sparrow  in  the  United  States  are  exam- 
ples. The  Califoi-nia  species  of  the  phylloxera,  an  aphis  or 
plant-louse  infesting  the  grape-vine,  was  introduced  into  France 
and  almost  destroyed  the  vines  of  that  country.  The  Russian 
thistle  at  one  time  threatened  to  overrun  the  wheat-fields  of  the 
Mississippi  basin,  and  the  strictest  means  are  necessary  to  keep 
it  under  control.  The  gypsy  moth,  whose  larvae  infests  ripening 
fruit,  has  attacked  the  orchards  of  the  New  England  States,  and  an 
expenditure  of  nearly  a  million  dollars  a  year  is  necessary  to  keep 
its  mischievous  woi'k  in  check. 


CHAPTER   X\Hl 

THE   GEOGRAPHIC    DISTRIBUTION   OF  PLANTS   AND 
ANIMALS 


Not  far  from  150,000  species  of  plant'  and  nearly  as 
many  of  animal  life  are  known  to  exist,  and  new  species 
are  discovered  yearly.  These  are  distributed  in  accordance 
with  the  laws  noted  in  the  previous  chapter — that  is,  they 
live  each  in  the  locality  best  adapted  to  it.  Plant  life 
inchides  species  that  vary  as  widely  in  form  and  structure 
as  the  multitude  of  animal  species. 

Distribution  of  Plants. — The  distribution  ^  of  vegeta- 
tion may  be  considered  in  several  aspects,  namely — alniu- 


FORESTRY   Ol     Till,    NORTHRRN    RKC.ION      OLD   GROWTHS   ANU 

315 


316  PHYSICAL   GEOGRAPHY 

dance  and  kind  ;  and  these  are  best  studied  with  reference 
to  their  regional  position  or  else  according  to  their  altitude. 
The  abundance  of  vegetation  is  governed  mainly  by  the 
conditions  of  temperature  and  moisture.  In  a  climate  that 
is  both  warm  and  moist  there  is  nearly  always  an  abun- 
dance of  vegetation.  Because  of  this  fact,  plant  life  is  most 
abundant  in  tropical  lowlands,  decreasing  as  the  latitude 
and  the  altitude  increase.  In  tropical  regions  it  is  profuse ; 
in  temperate  climate,  abundant ;  in  cold  regions,  scanty. 

With  reference  to  the  distribution  of  kind,  two  factors 
have  been  instrumental — environment  and  time.  In  the 
earlier  geological  ages  certain  species  seem  to  have  pre- 
vailed at  certain  centres,  and  from  these  they  have  spread 
in  various  directions.  The  area  over  which  the  species  of 
a  region  may  have  spread  is  a  question  chiefly  of  time ; 
the  locus,  one  of  environment.  The  vegetation  of  a  given 
region  is  called  its  fora. 

With  respect  to  distribution  the  map  on  page  318  shows 
that  five  centres  exist  from  which  species  have  spread,  or 
to  which  they  are  characteristic.^     Name  them. 

The  Northern  Regions,  Eurasian  and  American,  include 
the  greater  part  of  the  two  continents  north  of  the  Tropic 
of  Cancer  and  that  part  of  Africa  north  of  the  Atlas  Moun- 
tains. The  two  regions  contain,  as  natives,  a  large  number 
of  the  deciduous  trees,  gTains,  and  fruits.  The  grains, 
maize  excepted,  and  most  of  the  fruits  are  characteristic  of 
the  Eurasian ;  the  redwood,  sequoias,  sugar-cane,  tobacco, 
and  the  yuccas  to  the  American  region.  The  two  regions 
are  separated  by  the  Atlantic  Ocean,  and  though  the  life- 
forms  are  not  identical  they  are  very  similar. 

The  South  American  region  embraces  the  territory  south 
of  the  Tropic  of  Cancer,  both  mainland  and  insular.  The 
mahogany,  cinchona,  india-rubber,  and  rosewood  are  among 
the  chief  species  peculiar  to  the  region. 


DISTRIBUTION   OF  PLANTS  AND  ANIMALS    317 

The  African  or  Ethiopian  region  includes  all  of  Africa 
south  of  the  Atlas  Mountains  and  tropical  Arabia.  The 
baobab,  oil-palm,  euphorbias,  bigouias,  the  coffee-tree, 
several  heaths,  and  the  geranium,  are  among  the  native 
plants  peculiar  to  this  region. 

The  Oriental  Region  includes  the  territory  south  of 
the  Himalaya  Mountains,  and  most  of  Malaysia.  Among 
the  principal  characteristic  species  are  the  spices,  the 
ebony,  saudal-M'ood,  and  the  melons. 

The  Australian  Region  comprises  the  continent  of  Aus- 
tralia and  most  of  the  islands  east  and  north.  The  tlora 
of  this  area  is  highly  peculiar.  The  prevailing  color  of  the 
vegetation  is  bluish-green  and  the  leaves  turn  their  edges 
to  the  sun.  The  eucalyptus  or  gum  trees,  the  various  tree- 
ferns,  and  the  jarrah  are  peculiar  to  this  region.  In  the 
north  and  east  the  Australian  and  Oriental  regions  over- 
lap, and  are  marked  by  species  characteristic  to  both.  The 
Eucalyptus  and  the  tree-fern  have  been  introduced  into 
California ;  the  jarrah  is  much  used  in  the  manufacture  of 
street  paving-blocks. 

The  vei"tical  distribution  of  species  is  determined  by 
altitude.  Thus  at  the  base  of  the  Himalayas  and  the 
Andes,  the  flora  is  tropical ;  higher  up,  the  characteristic 
species  of  the  temperate  zones  replace  tropical  ]ilants ;  and 
at  an  altitude  of  twelve  thousand  feet,  more  or  less,  the 
vegetation  is  distinctly  that  of  polar  types. 

Economic  Plants. — Most  forms  of  plant  life  have  an 
imjiortaut  relation  to  mankind,  and  this  is  especially  true 
of  those  used  as  food,  as  medicine,  or  in  the  arts.  Chief 
among  them  are  the  grains  and  other  grasses,  tuberous 
plants,  fruits,  those  yielding  textiles,  and  tliosc  used  for 
building  tindjer. 

The  grasses  probably  extend  over  a  wider  area  than  any 
other  family.    Of  these  the  sugar-cane  and  niaiz<>,  or  Indian 


DISTRIBUTION  OF  x  LANTS  AND  ANIMALS    319 

coru,  are  native  to  the  American  coutiueiit.  All  the  others 
belong  to  the  Old  World,  but  have  followed  the  march  of 
mankind.  The  members  of  this  family  are  the  sole  food 
of  many  hundred  species  of  animals,,  and  the  seeds  are 
consumed  by  every  race  and  almost  every  tribe  of  man- 
kind. The  starch  they  contain  gives  them  their  chief 
value  as  a  food-stuif. 

Rice  is  confined  chiefly  to  the  marine  marshes  and 
swamp  lands  of  tropical  and  sub-tropical  regions,  but  there 
are  one  or  more  species  of  upland  rice.  Kice  is  the  staple 
food  of  about  one-half  the  people  of  the  world.  It  is  a 
notable  fact,  however,  that  in  certain  parts  of  China  and 
India,  wheat,  little  by  little,  is  supplanting  it.  Pound  for 
j)Ound  its  nutrient  value  is  not  equal  to  that  of  wheat. 
Maize,  or  Indian  corn,  a  native  of  the  New  World,  is  an  im- 
portant food-stuff  in  temperate  and  sulj-tropical  regions. 
It  is  the  chief  bread-ntuff  of  the  "  mixed  "  and  native  races 
of  the  New  Worhl.  In  the  United  States  and  Canada  it 
is  used  mainly  as  animal  food,  being  converted  into  pork. 
Its  use,  both  in  tlie  form  of  grain  and  meat,  is  largely  in- 
creasing among  the  peoples  of  the  Ohl  World.  It  is  also 
used  in  the  manufacture  of  liipiov. 

Wheat  is  the  l)read-stuff  of  the  civilized  peo])l('s  of  the 
temperate  zones  and,  is  the  fuel  of  the  activity  and 
energy  of  the  world.  It  is  grown  in  the  gieat  ])lains  of 
the  temperate  zones,  but  it  thrives  in  sub-tropical  and 
sub-polar  regions.  How  do  the  toj)ographic  features  of  a 
plain  affect  the  harvesting  and  transpoi-tation  of  wheat? 
How  do  they  affectthe  evolution  of  harvesting  machinery  V 

The  world  requires  about  2,200,000,000  bushelsof  wheat 
each  year,  and  the  amount  required  is  steadily  increasing. 
Why?  The  annual  crop  is  somewhat  gn-ater ;  in  ISD.S  it 
was  2,700,000,000  bushels.  It  is  estimated  that  the  maxi- 
mum   crop    p«^ssibl(!  is    not  far   from    twice   this  anionnt. 


320  PHYSICAL    GEOGRAPHY 

About  oue-fourtli  of  the  world's  crop  is  produced  in  the 
United  States. 

Rye  takes  the  place  of  wheat  in  many  countries,  and  is 
one  of  the  most  important  crops  of  Russia  and  Germany. 
A  species  of  oat  is  native  to  the  North  American  region, 
but  the  cultivated  plant  is  an  imported  variety.  It  is  a  fa- 
vorite food  for  horses.  Barley,  about  the  hardiest  of 
the  grains,  is  also  much  favored  as  a  food  for  horses,  but 
is  employed  mainly  in  the  manufacture  of  malt  liquors. 
Buckwheat  ^  is  not  a  wheat  at  all,  but  the  nut  or  fruit  con- 
tains a  large  percentage  of  starch  ;  hence  it  is  much  used 
as  a  f ood-stuif. 

The  canes  include  one  of  the  chief  sugar-producing 
plants.  ^  They  thrive  best  in  tropical  countries,  and  are 
extensively  cultivated  in  the  sub-tropical  belts.  In  oriental 
countries  the  bamboo,  a  species  of  cane,  is  much  used  as 
a  building  material  and  in  the  arts. 

The  palms,  next  the  grasses,  probably  yield  the  greatest 
variety  of  useful  products.  Cocoa-nuts,  dates,  sago,  sugar, 
wine,  and  oil,  are  all  derived  from  this  family.  So  far  as 
moisture  is  concerned,  the  palms  have  a  wide  range,  but 
in  respect  to  temperature  they  are  restricted  to  warm 
regions.     They  occur  in  both  hemispheres. 

Tuberous  plants  are  among  the  important  food-pro- 
ducers. The  potato,  probably  a  native  of  Chile,  has  been 
carried  to  every  part  of  the  civilized  world.  It  thrives 
best  in  temperate  latitudes. 

The  yam  ^  and  its  relative,  the  sweet  potato,  are  indige- 
nous to  tropical  America.  The  beet  and  the  turnip  are 
native  to  Europe.  The  former  is  now  the  principal  source 
of  sugar.  The  cultivated  onion  seems  to  have  come  from 
China,  but  a  wild  variety  occurs  in  America.  The  manioc 
(or  manihot)  is  native  to  tropical  America,  but  has  been 
transplanted  to  Asia  and  Africa. 


DISTRIBUTION   OF  PLAXTS  AXD  ANIMALS    321 

The  fruits  are  important,  not  only  as  delicacies,"  but  as 
foods.  Among  the  foremost  are  the  fig,  the  date,  and  tlie 
Corinth  grape.  They  are  native  to  the  basin  of  the  Medi- 
terranean Sea,  and  the  dried  fruit  is  a  n(>cessary  article  of 
food  in  that  region.  The  banana,  native  to  tropical  Asia, 
has  l^ecome  a  recognized  article  of  food  in  America. 

The  cultivated  varieties  of  the  apple,  pear,  peach,  and 
plum  are  native  to  western  Eurasia ;  the  cherry,  apricot, 
and  almond  to  the  eastern  part  of  that  continent.  The 
melons  and  their  near  relatives,  the  goiu-ds  (including  the 
pumpkin  and  squash),  are  also  from  Asia.  The  orange, 
lemon,  and  lime  probably  came  from  the  southern  slope  of 
the  Himalaya  Mountains.  So  far  as  written  history  is  con- 
cerned, the  grape  ^  has  a  greater  antiquity  than  any  other 
fruit,  manna  possilily  excepted.  It  is  found  in  a  wild 
state  in  both  hemispheres.  The  cranberry  j^robably  orig- 
inated in  the  temperate  zone  of  North  America,  migi'atiug 
thence  to  Europe.     The  tomato  is  also  native  to  America. 

Most  of  the  succulent  and  leguminous  plants,  such  as 
the  cabbage,  lettuce,  spinach,  and  peas,  have  followed  the 
migi'ations  of  Europeans.  The  bean  seems  to  have  come 
from  Egypt.  Celery  is  undoubtedly  of  Eurasian  origin  ;  it 
is  found  in  a  wild  state  over  a  large  part  of  the  continent, 
but  is  extensively  cultivated. 

The  beverage-yielding  plants  in  one  or  more  species  are 
cultivated  throughout  the  whole  civilized  world.  Tea  is 
sent  from  eastern  and  southeastern  Asia  to  almost  every 
other  country.  The  best  quality  is  grown  on  tlie  chain  of 
islands  east  of  the  mainland ;  it  is  also  grown  in  the 
United  States.  Coffee  is  probably  a  native  of  Abyssinia, 
but  is  now  cultivated  mainly  in  tin;  New  World.  It  grows 
wihl  in  the  former  n^gion,  and  a  similar  sjx'cies  is  native 
to  the  warm  parts  of  California. 

The  cacao-tree  yields   cocoa-beans.      Tiio   latter,  (iricd 


322  PHYSICAL   GEOGRAPHY 

and  browned,  uro  used  as  an  infusion ;  ground  with  its 
own  fat  or  with  hird  it  is  the  chocolate  of  commerce. 
It  is  native  to  trojiical  America.  Mate  {iiid-ta),  or  Para- 
guay tea,  is  the  leaf  of  a  species  of  holly  native  to  South 
America.  Its  infusion  is  used  all  over  that  grand  divi- 
sion. 

The  spices  come  nearly  all  from  Southern  Asia  and  the 
Malaysian  archipelago.  Of  these  none  except  pepper  has 
been  transplanted  to  any  great  distance  from  the  place  of 
their  nativity.  Capsicum,  or  red  pepper  {chile  Colorado), 
is  native  to  tropical  America.  Nutmeg  is  a  fruit,  the  cov- 
ering of  which  is  the  mace  of  commerce ;  cinnamon  is  the 
dried  inner  bark  of  a  species  of  laurel ;  cassia  is  a  similar 
species  growing  in  China  and  the  New  World ;  cloves  are 
the  dried  buds  of  a  tree  native  to  the  Molucca  Islands  and 
Southern  India. 

Medicinal  plants  are  as  widely  dispersed  as  is  the  hu- 
man race.  The  opium-poppy,  native  to  tropical  Asia,  pos- 
sibly to  Egypt,  has  not  migrated  far  from  the  j^lace  of  its 
birth.  The  cinchona,  a  native  of  South  America,  but  now 
cultivated  in  tropical  Asia,  yields  quinine  and  a  score  of 
derivatives.  The  various  members  of  the  night-shade 
family  '^  all  yield  powerful  medicinal  substances,  among 
them  nux  vomica,  strychnine,  belladonna,  and  gelsemium ; 
they  are  found  in  both  continents. 

Rhubarb  and  ginseng  are  native  to  China,  but  are  now 
cultivated  chiefly  in  the  United  States.  The  hemp  that 
yields  cannabis  indica,  or  hasheesh,  comes  from  south- 
ern Asia.  Coca  is  native  to  the  Andes.  Cascara  seems  to 
be  confined  to  tropical  and  sub-tropical  America.  Most 
medicines  widely  used  are  derived  from  plants  found  in 
tropical  regions.     Tobacco  is  native  to  America. 

Plants  used  in  the  arts  have  followed  man  in  his  migra- 
tions.    Cotton  ^°  is  the  furze  attached  to  the  seeds  of  the 


DISTRIBUTION  OF  PLANTS  AND  ANIMALS    323 

cotton  plaut.  Flax  aud  hemp  are  obtained  from  the  bark 
of  flowering  plants ;  both  came  from  the  Old  World — 
j^robabl}'  from  Africa — but  fonr-fifths  of  the  world's  prod- 
uct is  now  grown  in  the  United  States.  Jute  and  ramie 
are  native  to  Asia,  but  are  now  cultivated  in  America. 
More  valuable  than  either  of  these  is  pita,  the  fibre  of  the 
wild  pineapple,  native  to  America ;  and  so  also  is  hene- 
quen,  or  "  sisal  hemp,"  the  fibre  of  the  agave. 

The  forestry  of  the  world  is  distributed  with  a  remarka- 
ble degree  of  regularity-  The  pines  and  other  couifers, 
oaks,  elms,  maples,  willows,  chestnuts,  and  beeches,  occupy 
a  belt  between  the  40th  and  55tli  parallels  that  crosses 
both  continents.  The  distribution  of  tropical  forestry  is 
not  so  regular,  from  the  fact  that  South  America  has  a 
flora  peculiar  to  itself.  The  palm,  banana,  mahogany, 
bamboo,  and  representatives  of  the  pines  continue  through 
both  continents,  however. 

On  both  sides  of  the  belts  of  forestry  there  are  extensive 
treeless  areas.  In  some  instances  the  areas  are  treeless 
because  they  are  deserts,  but  in  others,  such  as  the 
prairies  and  plains  of  Eussia  and  the  United  States,  there 
is  a  fertile  soil  and  an  adaptability  of  environment.  In 
many  instances  there  are  no  trees  because  the  seeds  have 
not  ijeen  carried  thither  ;  because  the  rivers  and  the  winds, 
flowing  from  regions  that  practically  are  deserts,  carry  no 
seeds  into  the  regions  toward  which  they  flow. 

In  the  United  States  forestry  thrives  liest  in  a  gravelly 
soil,  but  lives  and  increases  in  a  sedentary,  prairie  soil. 
In  the  Champlain  period  that  followed  the  Glacial  epoch, 
the  northern  part  of  the  United  States  was  traversed  by 
streams  that  bore  the  seeds  of  various  species.  Wherever 
the  streams  deposited  gravel  they  also  deposited  seeds. 
Hence  this  region  was  sooner  or  later  covennl  with  trees. 
As  a  matter  of   fact,  the   timber-covered  regions  of   the 


324 


PHYSICAL   GEOGRAPHY 


northern  United  States  are  nearly  identical  with  the  area 
covered  by  stream  gravel  and  till. 

Distribution  of  Animals.— The  animal  life  of  a  region 
constitutes  its  fauna.  Of  the  various  classes,"  the  mam- 
mals represent  the  highest  types  of  life,  both  with  respect 
to  form  and  structure  and  also  in  the  matter  of  intelligence. 
All  the  forms  of  animal  life  possess  the  attribute  of  in- 
stinct— the  hereditary  power  of  thought  required  in  such 
actions  as  tend  to  preserve  and  extend  life.     The  higher 


THE   PENGUIN 
y4  type  of  Antarctic  life 

forms,  in  addition,  have  the  powers  of  reason.  These 
faculties  have,  doubtless,  largely  controlled  the  distribu- 
tion of  life. 

In  the  dispersal  of  animal  species  the  power  of  locomo- 
tion has  given  a  wonderful  development  to  both  instinct 
and  reason,  and  these  have  been  controlled  by  the  most 
powerful  motive  that  exists  in  connection  with  animate 
life,  namely — the  sense  of  hunger. 

As  in  the  distribution  of  plants,  there  seem  to  be  certain 
centres  from  which  animal  species  have  migrated.  But  the 
limits  have  been  determined  in  a  somewhat  different  way. 


326  PHYSICAL  GEOGRAPHY 

lu  the  case  of  plants  the  territory  of  a  flora  is  mainly  gov- 
erned by  environment ;  in  the  case  of  animal  life  environ- 
ment is  an  important  matter,  but  the  power  of  voluntary 
locomotion  has  been  the  leading  factor.  The  limits  of  a 
fauua,  therefore,  are  largely  determined  by  its  various 
physiographic  barriers. 

In  the  map,  page  318,  it  is  seen  that  the  North  Amer- 
ican and  Eurasian  regions  have  a  very  broad  extent,  and 
are  separated  by  marine  barriers  that  are  neither  very 
wide  nor  impassable.  In  the  south,  the  regions  are  sur- 
rounded by  barriers  that  practically  isolate  them.  For 
example,  South  America  is  separated  from  North  America 
by  the  barriers  of  sea  and  climate.  The  African  region  has, 
in  addition  to  these  barriers,  a  high  mountain  range  on  its 
northern  border ;  the  same  is  true  of  India,  south  of  the 
Himalayas ;  Australia  is  environed  by  the  sea  and  also  by 
peculiarities  of  climate. 

From  this  it  may  be  inferred  that  the  faunas  of  the  two 
northern  regions  are  not  greatly  dissimilar.  Such  an  infer- 
ence is  correct.  In  many  instances  the  species  are  identi- 
cal, and  in  others  an  order  or  a  class  has  its  representatives 
in  both  continents.  The  southern  regions,  however,  are 
marked  by  strong  contrasts. 

The  North  American  and  Eurasian  regions  have  in  com- 
mon many  species  of  carnivorous,  or  flesh-eating  animals. 
Various  species  of  wolf  and  bear  are  widely  dispersed 
through  both  regions,  and  the  cat  family  is  represented  by 
the  panther  and  several  species  of  wildcat.  Many  fur- 
bearing  animals — notably  the  lynx,  otter,  ermine,  badger, 
and  sable — are  common  to  both  regions,  and  so  are  species 
of  the  deer  family  and  mountain  sheep. 

The  grizzly  bear,  caribou,  bison,  musk-ox  and  black 
bear  are  peculiar  to  America ;  the  first  named  is  foimd 
only  in  the  Rocky  Mountain    highlands.     The   reindeer. 


DISTRIBUTIOX  OF  PLAXTS  AXD  AXIMALS     327 

camel,^-  buffalo,  and  nearly  all  domestic  animals  are  na- 
tive to  the  Old  World,  but  have  been  transplanted  to  the 
American  continent.  The  opossum,  puma,  bald  eagle, 
humming-bird  and  wild  tui'key  are  native  to  the  American 
region;  the  chamois,  ibex,  fallow-deer  and  aurochs  are 
peculiar  to  the  Old  World. 

The  South  American  Eegion  is  distinguished  by  a  pro- 
fusion of  animal  life.     The  monkevs  of  this  rescion  are  a 


W 


n 


I 


jriRN    (i[      I  Hi     SOUTH   AMERICAN   REGION:    SURVIVES   IN   THE   OLD   WORLD 


species  distinct  from  those  of  the  Old  World.  The  camel  " 
of  the  Old  World  is  here  replaced  by  the  alpaca,  vicuna, 
llama,  and  guanaco — all  distantly  related  to  the  camel. 
The  last  named,  however,  is  probably  native  to  the  South 
American  region. 

The  sloth,  armadillo,  ant-eater  and  peccary  are  peculiar 
to   this  region,  and  so  are  tlic  tiiiiihtous  j)aiToquets,  and  a 


328  PHYSICAL   GEOGRAPHY 

host  of  insect  life.  The  condor  is  the  nearest  approach 
to  the  European  vulture  and  the  rhea  to  the  ostrich. 

The  Ethiopian  Region  is  conspicuous  for  the  absence  of 
the  species  most  common  elsewhere.  On  the  other  hand, 
the  gorilla,  lion,  zebra,  hippopotamus,  giraffe,  ostrich,  iive- 
toed  elephant  and  many  other  characteristic  species  are 
found  nowhere  else.  In  but  one  other  region  is  the  pygmy, 
a  dwarfed  species  of  man,  fomid.^* 

The  Oriental  Eegiou  is  the  birthplace  of  most  of  the 
domesticated  animals.  Among  wild  animals  the  tiger, 
mongoose,  cobra,  and  three-toed  elephant  are  peculiar  to 
this  region.  The  rhinoceros,  jackal,  and  leopard  are  com- 
mon to  this  region  and  that  to  the  westward. 

The  Australian  Eegion  is  marked  by  the  most  unusual 
types  of  life  on  the  face  of  the  earth.  Almost  all  its  life- 
forms  are  peculiar,  and  but  few  types  found  elsewhere 
occur  in  this  continent.  Many  of  the  species  are  marsu- 
pials— that  is,  the  female  has  a  pouch  or  pocket  in  which 
the  immature  young  are  carried.  Many  others,  such  as 
the  kangaroos,  have  enormously  developed  hinder  legs. 
As  a  rule,  Australian  species  are  similar  to  those  of  a 
prior  geological  age. 

The  Bearing  of  Organic  Life  upon  Physiography. 
— In  the  foregoing  paragraphs  the  effects  of  physiographic 
forces  upon  life  have  been  considered.  The  bearing  of 
life  and  its  energy  upon  physiographic  forms  are  just  as 
far-reaching  and  quite  as  important. 

Life-forms  have  been  and  are  now  among  the  important 
agents  in  rock  formation.  Some  of  the  limestone  basins 
of  the  Mississippi  Valley,  all  the  infusorial  earths,  the 
various  fringing  reefs,  the  barrier  reefs,  the  atolls,  and  the 
encircling  reefs  are  the  work  of  animal  life.  On  even  a 
more  extended  scale  are  the  chalk  formations  of  Western 
Europe,  which  are  also  the  results  of  life. 


DISTRIBUTION  OF  PLANTS  AND  ANIMALS     32?) 

In  the  broad  areas  of  the  tropical  oceans  the  work  ot 
organic  life  is  of  still  gi-eater  magnitude.  The  water  of 
these  regions  is  swarming  with  life,  and  the  skeletons 
of  the  dead  forms,  together  with  other  mineral  constitu- 
ents, are  accumulating  at  the  bottom.     Wherever  deep-sea 


A  type  of  the  Auilralian  region 

dredging  has  been  carried  on,  these  accuniiil.ilioiis  h.ivc 
been  found. 

But  the  secretion  of  the  Hine  from  the  sc:i-\v,it(i-  li;is  li.id 
still  another  effect.  After  tlic  linx;  and  oilier  niim  r.il  ihmI- 
ter  has  been  absorbed  by  tin;  organism,  the  water  is  speci- 
fically lighter,  and,  as  a  result,  the,  ciiange  in  tiie  deii.sity 
of  the  Avater  has  brought  about  a  slow,  but  a  noric!  the  less 
certain  circulation  of  water. 


330  PHYSICAL   CxEOGRAPHY 

Vegetable  life  also  is  responsible  for  extensive  areas  of 
rock  formation.  Under  certain  conditions,  such  as  exces- 
sive saturation,  the  leaves,  twigs,  and  stems  of  plants  accu- 
mulate to  considerable  depths.  If  these  accumulations  be 
covered  by  overflowing  sediment,  either  fluviatile  or  ma- 
rine, the  wood-fibre,  after  long-continued  pressure  and  par- 
tial decomposition,  is  converted  into  coal. 

In  the  United  States  more  than  150,000  square  miles  of 
territory  are  underlain  by  coal  measures,  and  in  the  various 
basins  of  Eurasia  probably  a  greater  area  exists.  The  most 
extensive  formations  of  this  character  are  found  in  the  later 
rocks  of  the  Palgeozoic  age,  but  coal  is  not  confined  to 
any  particular  strata.  Coal-making  has  been  an  incident 
of  every  geological  age.  Diamond,  graphite,  anthracite, 
bituminous  coal,  mineral  pitch,  petroleum,  and  natural  gas 
are  all  the  results  of  organic  life. 

In  preventing  general  surface  erosion,  vegetation  has 
also  been  an  important  factor.  A  surface  covered  with 
grass  or  foliage  resists  the  action  of  rain  and  winds  alike. 
Covered  with  vegetation  a  surface  can  withstand  almost 
any  amount  of  wind  and  rain,  but  denuded  of  vegetation, 
the  surface  is  quickly  scored  by  running  water  ;  gullies 
grow  into  ravines,  and  the  latter  deepen  into  impassable 
canons. 

It  has  been  shown  in  another  chapter  that  not  only 
is  vegetation  capable  of  converting  a  moderately  dry  region 
into  a  sw^amp,  but  also  that  it  may  fill  the  swamp  and  after- 
ward reconvert  it  into  a  dry  region  again.  It  may  accom- 
plish even  more  than  this.  A  single  species,  such  as  the 
Russian  thistle,  may  exterminate  every  other  species  of 
plant  within  a  certain  area. 

As  the  native  vegetation  disappears  so  do  the  character- 
istic animals,  and,  sooner  or  later,  the  entire  flora  and 
fauna  are  changed.     This  changes  also  the  character  of 


DISTRIBUTION  OF  PLANTS  AND  ANIMALS    331 

the  soil ;  aud  as  the  topography  of  a  region  is  due  more  or 
less  to  its  characteristic  vegetation,  sooner  or  later  this  is 
changed. 

The  ver}-  lowest  forms  of  vegetable  life,  such  as  the 
moulds,  the  bacilli,  bacteria,  and  micrococci,  perform  an 
important  office  also.  These  forms,  commonly  known  as 
disease-germs,  may — and  sometimes  do — exterminate  whole 
species,  both  of  animals  and  plants.  In  company  with  the 
mosses  and  lichens  they  disintegrate  and  decompose  the 
hardest  rocks  and  crumble  them  into  soil.  In  warm,  moist 
regions  exposed  rock-clifi*s  and  strata  are  much  rarer  than 
in  arid  regions.  Fresh  surfaces  of  rock  once  exposed  are 
quickly  covered  with  mosses,  lichens,  and  the  various  pro- 
tophytes.  These,  once  estabUshed,  requu-e  time  only, 
either  to  completel}'  disintegrate  the  rock,  or  else  to  cover 
its  surface  to  a  considerable  depth. 

The  common  earthworm  plays  an  important  part  also. 
It  thrives  in  moist  earth,  and  a  colony  of  these  worms, 
once  bred  in  a  given  locality,  continues  to  inhabit  it  mitil 
the  whole  mass  is  changed  to  a  rich,  loamy  soil,  capable 
of  supporting  a  dense  vegetation.  Thus  it  is  seen  that  the 
lowly  and  often  invisible  forms  of  life  become  iinpttrtant 
factors  in  the  physiogi-aphy  of  a  region. 

QUESTIONS  AND  EXERCISES.— Make  a  list  of  the  forest  trees, 
shrubs,  and  other  wild  plants  growing  in  the  neighborhood  in  which 
you  live. 

Make  a  special  study  of  any  plant  or  "  weed  "  regarded  as  useless  or 
baneful.  If  you  cannot  obtain  the  information  you  require,  send  a 
specimen  to  the  Department  of  Agriculture,  Washington,  D.  C. 

Follow  the  same  directions  with  reference  to  the  animal  species,  es- 
pecially those  injurious  to  vegetation,  applying  to  the  Department  of 
Agriculture  for  information  you  cannot  obtain  elsewhere. 

Enumerate  the  articles  of  food  and  table  furniture  used  at  dinner,  and 
follow  the  route  of  each  one  from  its  native  place  to  the  table. 

Mention  the  various  uses  to  which  maize  or  the  corn  plant  is  put 
grain,  cob,  and  stalk. 


332  PHYSICAL   GEOGRAPHY 

In  what  ways  does  the  wheat  crop  affect  the  habitability  of  the 
United  States  ? 

Name  some  of  the  chief  causes  of  the  destruction  of  forestry.  Note 
an  instance  in  which  the  cultivation  of  the  cotton  plant  has  affected 
the  history  of  a  people. 

Describe  instances  in  which  the  distribution  of  animals  or  of  plants 
has  been  effected  by  the  agency  of  mankind. 


COLLATERAL   READING  AND    REFERENCE. 
Mill.— Realm  of  Nature,  pp.  303-320. 

NOTES 

'  These  are  grouped  in  five  sub-kingdoms.  17ie  protophytes  are 
the  lowest  form  of  vegetable  life.  They  consist  each  of  a  single 
cell  or  of  groups  of  cells.  In  this  sub-kingdom  are  included  the 
yeast  plant,  and  other  similar  substances  known  as  ferments,  the 
organisms  that  produce  all  the  forms  of  "rotting"  or  putre- 
faction, and  the  host  of  bacilli,  bacteria,  and  micrococci  (com- 
monly known  as  "microbes")  that  are  productive  of  disease  and 
various  structural  changes.  The  ThaUophytes  include  the  plants 
in  which  there  is  little  or  no  distinction  between  leaf  and  stem, 
such  as  lichens  and  fungi.  Nearly  all  the  "  sea- weeds  "  and  the 
vegetable  "moulds  "  belong  to  this  sub-kingdom. 

'Die  bryopliytes  comprise  the  mosses  and  the  liverworts.  Tlie 
pteridophytes  rank  a  little  higher.  They  include  the  club-mosses, 
horse-tail  rushes,  and  true  ferns.  All  the  foregoing  sub-kingdoms 
are  flowerless  ;  they  reproduce  by  means  of  minute  spores  that 
are  borne  in  receptacles  on  some  protected  part  of  the  plant.  The 
dust  coming  from  a  bursting  puflf-ball  consists  of  spores,  and  these 
have  the  reproductive  properties  of  .seeds  or  eggs.  The  phanero- 
gams include  all  the  species  of  grasses,  shrubs,  flowering  plants 
and  forestry.  Their  growth,  like  that  of  certain  lower  forms,  con- 
sists of  two  parts,  the  roots  and  the  aerial  portion.  They  repro- 
duce by  means  of  flowers  and  seeds. 

'This  term  is  used  here  because,  unfortunately,  it  is  almost 
universally  employed  in  the  science  of  geography.  What  really 
has  occurred  to  spread  the  species  is  a  migration  or  a  dispersal. 


DISTRIBUTION  OF  PLANTS  AND  ANIMALS    333 

'  This  classification  by  regions  or  centres  is  practically  the  sjiiiie 
as  that  proposed  by  Professor  Wallace,  except  that  the  names 
Eurasian,  North  American,  and  South  American,  are  substitu- 
ted for  pahvarctic,  iiearctic,  and  neotropical.  This  scheme  has 
been  adopted  because  it  is  based  strictly  upon  geographic  laws. 

*  Buckwheat,  for  convenience,  is  included  in  this  list.  The 
name  is  a  corruption  of  "  beech- wheat, "  on  account  of  the  resem- 
blance of  the  kernel  to  that  of  the  beech-tree.  It  is  said  to  have 
been  introduced  into  Europe  by  the  Saracens,  and  in  parts  of 
Europe  it  bears  the  name  Saracen  wheat.  It  probably  came 
from  Manchuria. 

^  To  these  should  be  added  the  beet,  wliich  is  now  extensively 
cultivated  for  the  purpose  of  sugar-manufacture.  In  tropical 
America  certain  agaves,  near  relatives  to  the  grasses,  are  the  source 
of  not  a  little  sugar. 

^The  yam  is  found  also  in  the  East  Indies,  and  it  is  a  disputed 
(juestion  whether  or  not  the  American  species  is  a  descendant  of 
that  of  India. 

'  This  fruit  is  commonly  but  incorrectly  known  as  a  i-urrant. 
The  latter  is  regarded  as  native  to  Eurasia,  but  wild  species  are 
certainly  indigenous  to  western  North  America.  The  apple  ivnd 
the  plum,  said  to  be  native  to  Eurasia,  are  also  found  wild  in 
North  America.  The  peach  seems  to  have  originated  in  Persia, 
from  which  the  name  is  derived. 

'The  fox  grape,  a  wild  fruit  growing  in  Canada  and  the  New 
England  States,  was  discovered  and  described  by  the  Noi-se  ex- 
plorers who  visited  North  America  about  a.d.  1000.  The  culti- 
vated species  of  America  are  mainly  imported  ;  the  Concord  is  an 
improved  wild  species  of  America. 

"The  potato,  tomato,  and  tolKicco  are  the  most  important  .\Mieii- 
can  representatives  of  this  family.  The  "jimson"  (probably  a 
corruption  of  Jamestown)  and  other  species  of  tiie  datura  stramo- 
nium are  found  in  all  moist  and  warm  regions  of  Nt)rth  .\merica. 

'°  Barbados  and  Sea-Island  cotton  are  native  to  America. 

"  The  classification  of  animals  is  somewhat  more  ditllcnlt  tliaii 
that  of  plants.  The  animal  kingdom  is  divided  into  eight  great 
branches  or  groups  ;  these  are  again  divideil  into  dasM-s  and  sub- 
divided into  the  following  orders  : 

Protozoans,  the  lowest  forms  of  animal  life,  such  as  rhizopods. 
infusoria.     Porifera,  of  which  the  sponges  are  the  ciiief  »pecie». 


334  PHYSICAL   GEOGRAPHY 

Ccelenterates,  of  which  the  coral-polyps,  jelly-fish,  and  sea- 
anemones  are  the  best  types.  Echinoderms,  represented  by  the 
star-fishes,  sea-urchins.  Vermes,  or  true  worms.  Mollusks,  or 
shell-fish,  such  as  the  oysters,  clams,  limpets,  snails,  and  slugs. 
Arthropods,  including  the  types  of  lobsters,  crabs,  spiders,  scor- 
pions.     Vertebrates,  or  animals  having  the  back-bone. 

Of  these  the  first  four  inhabit  the  water  ;  the  remainder  include 
both  land  and  water  animals.  The  vertebrates  comprise  various 
classes  of  which  the  principal  are  mamtnals,  or  warm-blooded 
animals  that  suckle  their  young  ;  birds,  mainly  aerial  in  their 
habits  ;  reptiles,  including  snakes,  lizards,  and  turtles  ;  batra- 
chians,  represented  by  frogs  and  toads,  mudfishes — all  aquatic  in 
their  habits. 

'■^  The  factors  that  have  governed  the  dispersal  of  animal 
species  cannot  always  be  determined.  It  must  be  borne  in  mind 
that  dispersal  began  in  prior  geological  times,  when  the  condi- 
tions of  environment  were  often  different  from  those  of  the  pres- 
ent age.  In  the  case  of  marine  life,  the  limits  to  the  territory  of 
species  are  bounded  mainly  by  the  temperature  of  the  water. 
The  fauna  of  cold  currents  is  materially  different  from  that  of 
warm  waters.  Deep  sea  species  are  wholly  different  from  surface 
species  also.  The  fish  living  at  the  bottom  of  the  deeper  parts  of 
the  sea  are  mainly  sharks,  several  new  species  of  which  were  dis- 
covered by  the  Prince  of  Monaco  at  a  depth  of  two  miles. 

'^  The  camel  probably  originated  in  America,  but  became  ex- 
tinct before  the  Glacial  Epoch.  In  1858  it  was  introduced  into 
the  Basi-n  Region  of  the  United  States  and  a  few  head  still  sur- 
vive in  the  Gila  Desert  of  Arizona.  The  popular  distinction 
between  the  camel  and  the  dromedary  is  a  very  misleading  and 
an  incorrect  one.  The  latter  term  (from  a  Greek  word,  to  run, ) 
first  applied  to  a  species  remarkable  for  fleetness,  afterward  came 
to  include  any  camel  trained  to  tteetness  of  movement. 

'^  There  is  some  evidence  of  the  existence  of  pygmies  in  Europe 
during  the  neolithic  period,  and  x-ecent  discoveries  in  Switzer- 
land strongly  confirm  the  evidence.  Dr.  E.  M.  Aaron  has  called 
attention  to  the  fact  that  the  archaeological  records  of  Cozumel, 
an  island  east  of  Yucatan,  bear  evidence  of  the  existence  of  a 
pygmy  race.  The  ruins  of  the  diminutive  store-houses  that  are 
still  found  on  the  island,  and  the  small  human  skulls  lend  credi- 
bility to  the  theory  of  pygmy  existence  in  America. 


CHAPTER  XIX 

MAN 

Man,  though  at  the  head  of  animate  creation  so  far  as 
the  development  of  reasoning  powers  are  concerned,  from 
a  physiological  stand-point  is  distinctly  an  animal,  and  is 
closely  related  to  other  vertebrates.'  The  skeleton  of  a 
man  does  not  differ  materially  in  structure  from  that  of 
a  monkey,  a  bear,  a  dog,  or  a  bat ;  it  does  not  differ  very 
greatly  from  that  of  a  whale,  a  lizard,  or  a  bird ;  it  closely 
resembles  that  of  the  gorilla. 

With  respect  to  nutrition  the  resemblance  is  still 
stronger.  The  digestive  apparatus  and  the  various 
processes  by  which  food  is  converted  into  blood,  bone, 
and  flesh  are  the  same  in  man  as  in  other  mammals. 
The  food,  moreover,  is  practically  the  same — water,  grain, 
fruit,  and  the  flesh  of  other  animals.  The  organs  by 
which  the  blood  is  circulated  are  the  same,  and  the  proc- 
esses involved  in  breathing  do  not  differ  in  any  essential 
l)oint  in  man  and  other  mammals.  In  the  structure  of 
bone,  muscle,  and  tendon,'  and  in  the  operation  of  s])ecial 
organs,  such  as  nerves,  intestines,  lungs,  and  heart,  the 
functions  ai-e  practically  identical. 

The  chief  characteristic;  of  mankind  is  the  great  develop- 
ment of  the  reasoning  faculties.  Tlie  power  of  reason  is 
certainly  common  to  some  of  tlu;  lower  animals — possibly 
to  all  species.  In  man,  however,  this  fjiciiUy  is  enormously 
developed  in  comparison  witli  other  animals.  Moreover, 
the  power  of  reasoning  al)stractly  seems  to  \h)  poss«'ss<'d 
by  no  other  species  of  life. 

3;{5 


336 


PHYSICAL   GEOGEAPHY 


The  classification  of  mankind  into  races  and  families, 
however,  is  one  of  such  great  difficulty  that  no  two  eth- 
nographers are  in  full  agreement.^  Color  of  skin,  texture 
of  hair,  and  language  have  been  each  made  the  basis  of 
classification,  but  each  system,  when  closely  followed,  leads 
to  confusing  difficulties. 

The  Black  Peoples. — The  people  of  this  type  are 
characterized  by  black  skin,  kinky  or  woolly  hair,  and  thick 

lips.  The  Negroes  are 
the  best  known  people  of 
the  type.  This  race  is 
native  to  Central  Africa, 
but  has  been  acclimated 
in  America,  numbering 
there  about  ten  or  twelve 
millions.  The  Bantus  are 
the  finest  specimens  of 
'Iv  the  black  type,  and  iu; 
their  native  region  are 
approaching  civilization. 
They  are  distinguished 
by  a  color  of  skin  that  in  some  cases  is  distinctly  bronze 
rather  than  black.  Their  features  are  finer,  and  the  lips 
thinner  than  those  of  the  Negro. 

The  Australasians  inhabit  the  continent  of  Australia  and 
the  near  islands.  They  are  tall  and  slender,  have  straight 
hair,  and  represent  the  lowest  degree  of  civilization.  The 
Melanesians  are  native  to  New  Guinea  and  the  chain  of 
islands  to  the  southeast.  There  are  also  tribes  in  various 
parts  of  the  Philippine  Islands.  The  Melanesians  and 
Australasians  are  also  called  "Negroids."  They  are  sav- 
ages, warlike  and  ferocious.  Cannibalism  is  almost  uni- 
versally practised  among  them,  but  is  not  confined  to  the 
black  races. 


THE    BLACK   TYPE :    A    SAVAGE 


MAN 


33: 


The  black  type  of  mankind  is  best  adapted  to  a  warm 
climate,  and  the  various  races  are  free  from  the  malarial 
fevers  and  other  baneful  climatic  influences  that  are  so 
fatal  to  white  peoples.  In  tropical  regions  the  Negro  races 
are  bj'  far  the  most  enduring  peoples.  The  religion  of  al- 
most all  the  people  of  this  type  is  fetich  or  obeah  worship. 

The  Yellow  Peoples. — The  yellow  or  Turanic  peoples 
are  probably  native  to  Asia  somewhere  north  of  the 
Himalaya  Mountains.  The  type  is  characterized  bj 
coarse    and    straight   black  hair,    high    cheek-bones,    and 


AMERICAN    INDIANS 


yellow  or  yellowish-brown  skins.  In  some  instances,  as 
the  Chinese,  the  eyes  are  set  at  a  peculiar  angle,  giving 
rise  to  the  term  "  almcmd-eyed." 

Chief  among  yellow  peoples '  are  the  Chinese,  I'lirmese, 
Anamese,  and  Siamese.  Tiie  civilization  of  tiie  Cliinese 
IS  an  old  one  and  highly  ehiborated.  In  religi»)n  they  are 
noniiiially  Buddhists,  but  in  fact  they  tirr.  given  ehi«ll\  to 
ancestor-worship.  The  Tibetans  represent  the  I  test  exam- 
])les  of  the  race.  The  Burmese,  Anamese,  and  Siamese 
are  pure  Buddhists.  The  Mongols  of  western  and  noiiliein 
Asia,  especially  the  high   phiteaus,  are  a  race  of  noina.be 


338  PHYSICAL   GEOGRAPHY 

horsemen,  courageous  and  intelligent,  but  only  a  remove 
from  the  savage  state.  In  religion  they  are  Mohamme- 
dans. The  otishoots  of  this  race  that  have  settled  in 
Europe — the  Turks,  Huns,  Laps,  and  Finns — have  reached 
a  high  degree  of  civilization. 

The  Japanese  are  probably  a  mixed  race — ^Mongol  and 
Malay,  with  which  possibly  there  has  been  absorbed  a  still 
older  race,  native  to  the  islands.  Intellectually  the  Japa- 
nese are  at  the  head  of  the  race  which  they  represent,  and 
within  fort}^  years  they  have  developed  a  civiHzation  com- 
paring favorably  with  that  of  European  nations. 

The  Malays,  or  brown  race,  inhabit  southeastern  Asia, 
and  the  islands  to  the  eastward.  In  their  present  state 
most  of  them  are  savage,  but  they  seem  to  have  the  capa- 
bilities of  an  advanced  civilization — a  fact  apparent  in  the 
Japanese,  Javanese,  and  Hawaiians.  The  Maoris  of  New 
Zealand  are  an  excellent  type  of  Malay.  The  Hovas  ^  of 
Madagascar,  belong  to  this  race.  Most  of  the  native  peo- 
ples of  the  Philippine  Islands  are  Malays.  The  Tagals 
have  reached  a  condition  of  civilization ;  the  Visayas  and 
Maccabeles  are  but  little  inferior  ;  the  Moros  are  savages. 

The  American  "Indians,"  for  the  greater  part  charac- 
terized by  a  brown  color,''  are  native  to  the  American 
continent.  At  the  time  of  the  discovery  of  America  several 
tribes,  such  as  the  Aztecs  and  Peruvians,  were  emerging 
from  a  state  of  barbarism  into  one  of  civilization.^  They 
were  gradually  absorbed  by  their  conquerors. 

In  South  America  and  Mexico  the  Indians  have  become 
a  mixed  race.  For  the  greater  part,  this  has  resulted  from 
inter-marriage  Avith  the  Latin  races — especially  the  Portu- 
guese and  Spanish.  In  North  America,  on  the  contrary, 
where  the  associations  between  Indians  and  Teutonic 
peoples  have  always  been  marked  by  bitter  hatred,  the 
Indian  blood  is  still  pui-e. 


?40 


PHYSICAL   GEOGRAPHY 


The  Eskimos,  one  of  tlie  most  interesting  divisions  of 
the  yellow  type,  are  coutinecl  to  the  north  circumpolar 
regions.  They  seem  to  be  related  to  some  one  or  other  of 
the  Mongol  races,  but  the  relation  is  distant.  They  are 
short  in  stature,  averaging  less  than  five  feet  in  height. 
They  are  intelligent  and  highly  susceptible  to  civilization. 
This  fact  is  unusual,  inasmuch  as  their  habitations  are  mud 
and  stone  huts  ;  their  occupation,  fishing;  and  their  food, 

raw  blubber  and  fish. 

The    White    Peo- 
ples.— This  race  com- 
prises two  great  divis- 
ions,  each  subdivided 
into    various    families. 
These  divisions,  more- 
over,    represent      lan- 
guage     and     relation, 
rather  than   structure. 
The  color  of  the  skin 
varies    from    light 
blonde     to    swarthy, 
closely    approximating 
black     among    certain 
peoples.      Intellectual- 
ly,  it  is  the  dominat- 
ing type  of  mankind. 
The   Aryan  division   is  by  far  the  most  Avidely  spread^ 
and   numerous   of   the   type.     In   Asia,   it   includes    the^ 
Hindus,  the  Persians  and  most  other  dwellers  in  the  Iran^ 
plateau.     In  Europe,  it  includes  almost  the  entire  popula* 
tion,  the  Turks,  Huns,  Lapps,  Finns  and  Semitic  peoples 
excepted.    In  the  American  continent,  to  which  its  peoples 
have  migrated,  it  embraces  about  one  hundred  millions  of 
souls,  mainly  of  the  Teutonic  family. 


WHITE   TYPE  ;    LATIN 


MA?^ 


341 


The  Teutonic,  Latin,  Sclavonic,  and  Keltic  families  of 
this  race  now  constitute  the  leading,  most  intellectual,  and 
most  poAverful  nations  in  the  world.  These  families  occupy 
most  of  Europe  and  the  greater  part  of  North  America. 
Here  the  peoples  of  the  various  families  are  confusedly 
mixed  by  intermarriage.  In  South  America  they  liave 
intermarried  Avith  the 
native  races. 

The  Semitic  family 
comprises  the  Hebrews, 
Moors,  Arabs,  and  Abys- 
sinians.^  The  Assyri- 
ans and  the  Phoenicians 
were  also  of  this  race, 
but  they  have  been  ab- 
sorbed, or  dispersed  by 
conquest.  The  Hebrews 
or  Jews  are  the  only 
siu'viving  remnant  of 
this  race  now  holding  a 
position  of  any  im- 
portance. For  about 
four  thousand  years, 
in  spite  of  fearful  odds 
against  them,  they  have  held  a  commanding  position. 

''springing  from  a  family  whose  native  place  was  not  far 
from  Syria,  the  Jews  became  a  nation  of  considcrabh>  im- 
portance. Because  of  their  steadfastness  to  th.-ir  rrligicn, 
neither  slavery  nor  conquest  has  oxterminat(><l  tli.iii.  Dif- 
fused over  the  earth,  they  are  numerically  ab..iit  as  strong 
as  ever  they  were,  and  th(ur  religion  and  (•rivm..nial  rites 
are  as  marked  to-day  as  they  \swv.  four  thousan.l  yars  ago. 

Pygmies.— Scattered  over  a  i sid.Tablr  -.um  of  Africa 

are  peoples  having  no  ethnographi.-  coi.n.cti.Mi  or  ivlati.m 


\V 


WHITE   TYPE  :    A    REPRESENTATIVE   OF 
THE    Hir.HEST    CIVII.IZATION 


342 


PHYSICAL   GEOGRAPHY 


to  any  of  the  foregoing  families.  These  are  the  pygmies.' 
So  far  as  the  color  of  the  skin  is  concerned,  there  are  two 
classes  of  this  people — one  having  a  light  brown  skin,  the 
other  being  almost  black. 

Of  the  various  pygmj^  tribes  the  best  knoAvn  are  the 
Akka,  Wambntti,  and  Batua  of  central  Africa,  and  the 
Bushmen  of  tlio  soiitliorn  part.  All  individuals  are  charac- 
terized by  a  heavy  growth 
of  rusty,  red-brown  hair 
upon  the  bodies,  prog- 
nathic jaws  and  retreat- 
ing foreheads.  The  aver- 
age stature  of  the  Bush- 
men is  about  five  feet ; 
of  the  other  tribes  about 
four  and  one-half  feet. 
The  Akka  are  character- 
ized by  mis-shapen  bod- 
ies, long,  skinny  fingers, 
and  withered  legs.  The 
Negroids  of  the  Philip- 
pine Islands  are  some- 
times classed  among  the 
pygmies. 

Nearly  all  the  pygmy 
tribes  have  learned  the 
use  of  fire,  but,  as  a  rule,  they  eat  their  food  raw.  Although 
they  have  a  very  low  place  in  the  human  scale,  they  display 
considerable  intelligence.  The  AVambutti  are  ingenious 
in  devising  nets  and  traps  for  securing  game,  and  they 
seem  capable  of  a  low  form  of  civilization.  The  pygmies 
are  rarely  at  war  either  with  the  other  African  tribes  or 
with  one  another. 

Antiquity  of  Man. — The  written  history  of  man  does 


MAN 


343 


not  extend  backward  more  than  six  thousand  years  before 
the  Christian  era,  and  of  this  period  the  first  half,  as  re- 
corded in  Holy  Scripture,  contains  data  concerning  but  one 
or  two  famihes  and  their 
descendants.  Geologi- 
cal history  goes  back  to 
a  period  of  greater  an- 
tiquity, but  unfortunate- 
ly gives  no  clew  where- 
by the  age  of  man  can 
be  computed  in  years. 
Written  history  did  not 
begin  until  man  had 
reached  a  comparatively 
high  state  of  civiliza- 
tion, but  geological  his- 
tory antedates  this  pe- 
riod, and  discovers  man 
living  practically  in  a 
wild  state,  as  a  hunter 
and  a  dweller  in  caves. 

If  man  preceded  the 
Glacial  epoch,  about 
every  trace  of  the  spe- 
cies disappeared.  With 
a  few  exceptions,  upon 
which  doubt  has  been 
thrown,  the  oldest  traces 
of  mankind  are  found 
just  above  the  unsorted 
drift   of   the    Glacial 

epoch,  and  below  that  of  the  river  gravels  of  Clianiplain 
times.  Above  the  glacial  drift,  however,  tiiore  can  1>.-  no 
doubt  of  the  existence  of  th(!  sp(>ci<!S.'" 


VF.II.OW   TVPF.     JAPANRSE. 


344 


PHYSICAL   GEOGRAPHY 


Both  in  Europe  and  America  the  bones  of  man,  associ- 
ated with  those  of  the  cave-dwelling  auimals  he  hunted, 
have  been  abundantly  found.  With  these  have  been  found 
also  implements  of  the  chase,  ornaments,  charred  pieces  of 
bone,  and  in  one  instance  a  rude  drawing  of  an  extinct 
species  of  elephant,  sci'atched  on  ivor}'." 

From  the  time  of  the  earliest  geological  history  of  the 
species,  there  is  observable  one  feature  that  distinguishes 


.#« 


1^  p..^>r-      -.'^ 


EMERGING  FROM  A  SAVAGE  STATE 


mankind  from  brute  creation,  namely — raj)id  intellectual 
development.  Primitive  man  had  learned  the  use  of  fire, 
and  this  in  itself  was  to  give  him  supremacy  over  all  other 
animate  nature.  He  had  also  acquired  the  use  of  tools,  and 
these  were  a  great  increase  of  power.  The  earliest  race  of 
people  employed  hammers  or  axes  of  rough  stone.     The 


MAN  345 

next  step  seems  to  have  been  the  making  of  polished  stone 
axes,  knives,  arrow-heads,  etc.  AVhen,  however,  the  primi- 
tive man  applied  fire  to  the  shaping  of  his  tools  and  imjile- 
ments  made  of  metal,  his  civilization  was  assured,  and  his 
power  became  supreme. 

At  first  the  metal  employed  was  a  crude  alloy  now  kuowu 
as  bronze.  At  a  later  period,  however,  iron  was  substitu- 
ted for  the  alloy.  Some  of  these  implements  were  of  an 
ornamental  character,  but  in  the  main  they  were  either 
tools  or  weapons.  AVith  the  increased  power  ati'orded  by 
these  tools  the  people  who  used  them  pass  out  of  the  state 
of  savagery  and  emerge  into  that  of  civilization. 

Migrations  of  Mankind. — The  history  of  maukiud  is 
the  history  of  successive  migrations  that  have  been  going 
on  for  more  than  four  thousand  years.  From  the  earliest 
times  people  have  associated  in  families,  families  have 
grown  into  clans,  and  clans  into  tribes.  When  a  region 
has  been  sparsely  settled,  association  and  governmeut  have 
commonly  been  of  the  patriarchal  kind,  the  oldest  one  of 
the  family  or  clan  being  the  leader. 

In  cases,  however,  where  there  has  been  a  common 
enemy,  the  plan  of  association  has  often  been  communal 
as  well  as  tribal.  Thus  while  the  families  described  in  the 
earlier  history  of  the  Old  Testament  observed  a  patriarchal 
rule,  in  later  times,  the  plan  of  governmeut  became  com- 
munal and  afterward  national.  The  same  evolution  had 
began  in  the  case  of  the  aboriginal  Americans.  Families 
had  grown  into  clans  and  tribes, and  among  the  Aztecs  and 
Peruvians,  tribal  association  had  grown  into  connuuiud 
government  and  was  fast  emerging  into  civilization. 

But  there  have  always  been  limits  to  the  growth  of  a 
people.  They  may  be  exterminated  by  a  stronger  race; 
they  may  be  dispossessed  by  a  stronger  ])eoi)lo  or  be  al)- 
sorbed  by  them;  or  they  may  fin. 1  the   region  too  much 


346 


PHYSICAL   GEOGRAPHY 


overstocked,  aud  incapable  of  supporting  so  great  a  popu- 
lation. In  any  case,  unless  the  people  is  exterminated  or 
absorbed,  migration  is  the  only  remedy. 

Thus,  tribes  of  the  Tartar  ^^  race,  known  in  history  as 
the  Huns,  migrated  from  the  plateaus  of  Asia  and  over- 
ran a  large  part  of  Europe.     On  their  way  they  drove  the 


THE    HABITATlONb    UP    A   BARBAkUUb    PbOPLE 


eastern  Goths  from  their  lauds,  aud  the  latter,  in  turn,  over 
whelmed  Italy  and  Spain.  The  Lombards,  a  Teutonic 
people,  migrated  from  the  shores  of  the  Baltic  to  the  iVdri- 
atic  Sea.  The  Vandals  swept  over  western  Europe,  leaving 
behind  a  trail  of  fire  and  blood.  They  devastated  Spain, 
crossed  to  Africa,  and  established  an  empire  on  the  site  of 
Carthage.  About  one  hundred  years  later  they  were  exter- 
minated by  a  Koman  army.    Under  the  teachings  of  Islam, 


MAN  347 

the  Arabs  (or  Saracens)  devastated  the  north  of  Africa, 
entered  Spain  and  penetrated  France.  They  founded  a 
Moorish  empire,  but  were  afterward  driven  from  Europe. 

The  foregoing  are  but  a  few  of  the  movements  of  popu- 
lation that  occui-red  in  the  short  space  of  three  centuries, 
and  in  the  smallest  natural  division  of  land.  History  takes 
no  note  of  similar  changes  that  must  have  been  going  on  in 
other  parts  of  the  world  at  the  same  time. 

The  records  of  unwritten  history  furnish  many  instances 
of  the  dispersions  of  peoples  that  must  have  taken  place 
on  a  considerably  greater  scale.  In  some  instances  the 
migration  was  a  systematic  movement  that  practically  was 
the  advance  of  an  army  ;  in  other  instances  it  was  a  grad- 
ual extension  of  limits. 

The  migration  of  the  Aryan  race  is  an  illustration  of 
systematic  dispersion.  From  some  part  of  Eurasia  the 
various  families  of  this  race  wandered  westward  imtil  they 
occupied  all  Europe.  From  Europe,  moving  still  westward, 
they  have  suljjugated  the  American  continent,  and  even 
now  the  advance  guard  is  knocking  at  the  doors  of  Asia, 
after  nearly  completing  the  circuit  of  the  world.  There 
can  be  but  one  explanation  of  such  a  wonderful  disper- 
sion. It  is  the  straggle  for  existence — the  energy  put  forth 
to  appease  the  cravings  of  hunger. 

Man's  Relation  to  Physiography. — The  influence  of 
man  as  a  g<;<)gr;i[)]iie  ag«int  is  ot'tt-n  overlooked  and  the 
far-reaching  consequences  are  seldom  appreciated.  These 
effects  may  be  classified  as  interference  with  tin?  ordinary 
course  of  natural  events,  in  rcspet-t  to  tlie  surface  of  the 
land,  with  respect  to  climate,  with  referenda  to  drainage, 
and  in  the  dispersion  oi  life. 

The  sui-face  of  the  land  has  l)cen  iiiodilietl  by  man  in 
many  ways.  Of  these  the  most  important  is  the  destruc- 
tion of  forestry.     In  both  Europe  and  the  United  Stattis 


348  PHYSICAL   GEOGRAPHY 

a  very  large  part  of  the  surface  once  forest-clad  is  now 
bare.  By  various  artifices,  running  streams  have  been 
made  to  cover  enormous  surfaces  with  fluviatile  deposits, 
and  by  the  same  process  immense  volumes  of  soil  have 
been  removed  from  one  place  to  be  transported  to  another 
and  more  available  locality. 

Piers  and  sea-walls  have  been  built  in  such  places  as  to 
extend  shores  to  a  considerable  distance  seaward.  Thus, 
nearly  one-third  the  area  of  the  Netherlands  has  been 
reclaimed  from  the  ocean ;  Venice  has  become  a  city  of 
the  mainland;  and  considerable  areas  of  Chicago,  New 
York,  Boston,  and  San  Francisco  are  built  upon  land  that 
has  been  made  by  the  industries  of  man. 

The  various  highway's,  roads,  railways,  and  canals,  to- 
gether with  the  levelling  and  filling  that  accompany  the 
growth  of  cities  and  towns,  form  a  permanent  record  of 
mankind.  More  than  this  even,  is  the  surface  covered  by 
the  rubbish  carted  from  cities  and  spread  here  and  there. 
It  is  estimated  that  the  surface  of  Jerusalem  has  been 
buried  many  feet  by  the  accumulating  rubbish.  In  places, 
the  city  of  Rome  has  been  filled  forty  feet  deep,  and  the 
same  result  has  obtained  in  the  vicinity  of  other  cities. 

By  the  diversion  of  drainage,  swamps  have  been  changed 
to  dry  land  and  their  flora  entirely  replaced  by  other 
species.  By  canals  and  ditches,  lakes  have  been  drained 
and  the  lake  basins  given  up  to  cultivation.  By  systems 
of  levees  and  jetties,  river-basins  have  been  limited  in  area, 
and  the  area  of  sediment-depositing  has  been  changed  from 
one  place  to  another. 

Perhaps  the  most  important  changes  that  have  resulted 
from  the  hand  of  man,  however,  are  connected  with  the 
dispersal  of  life.  Through  his  agency  various  species 
have  been  transported  to  all  habitable  parts  of  the  earth  ; 
many  species  have  become  extinct,  and  the  habits  of  still 


MAN  349 

others  have  been  greatly  changed.  It  requires  only  a 
brief  geological  period  until  the  interference  of  man  shall 
prove  to  be  one  of  the  most  important  of  ph3'siographic 
agents. 

QUESTIONS  AND  EXERCISES.— Why  will  not  the  ordinary  lawa 
concerning  the  distribution  of  life  apply  to  the  dispersal  of  man  ? 

Make  a  list,  as  complete  as  you  can,  of  the  various  races  and  families 
now  in  the  United  States  ;  from  what  part  of  the  world  did  each  come  ? 

Name  the  advantages  possessed  by  man  over  other  species  in  over- 
coming the  restrictions  imposed  by  his  environment.  In  what  ways 
can  he  override  such  barriers  as  the  sea,  deserts,  polar  regions,  and 
regions  not  habitable  by  other  species  ? 

How,  and  in  what  instances,  has  the  discovery  of  gold  affected  the 
migration  and  dispersal  of  man  ? 

Mention  one  or  more  instances  in  which  this  dispersal  has  been  caused 
by  an  enemy. 

COLLATERAL   READING   AND   REFERENCE. 

Shaler. — Nature  and  Man  in  North  America. 
Mill.— Realm  of  Nature,  pp.  320-327. 
Marsh.— The  Earth  as  Modified  by  Human  Action. 
MiXDELEFF.— Migrations  of  the   Cliff  DweUers— Bureau  of 
Ethnology. 

Dexiker.— Races  of  Man,  pp.  45G-4G6. 


NOTES 

'Man  is  the  only  animal  thut  habitually  walks  en-ct  that  is. 
with  the  spinal  coluuin  perpendicular  to  the  plane  of  the  feet. 

'  Healthy  lunjr  tissue,  or  that  of  the  heart,  tiie  liver,  the  uniwle 
are  so  closely  alike  in  structure  that  a  section  from  out-  animaL 
serves  perfectly  as  an   illustration  of  the  corn'spoiidiiij^  tissue  of 

another. 

'The  futility  of  even  the  most  ciirefully  made  classilicaf ion  in 
apparent  when  one  considers  the  various  interbn^'dinu'  and  amal- 
gamation of  races.  For  instance,  the  Romanic  fandiy  cmbnicen 
the  five  peoples  enumerated   in   the  foregoing  fable.      Hut    the 


350  PHYSICAL   GEOGRAPHY 

Romans  were  a  mixture  of  Latins,  Sabellians,  and  Etrurians,  only 
one  element  of  which  is  known  certainly  to  be  of  Aryan  descent. 
An  infusion  of  Greek  blood  developed  the  fighting  powers  of  the 
mixed  race,  and  led  to  the  conquest  of  the  greater  part  of  Europe. 
When  the  Western  Empire  had  broken  into  fragments,  the  Latin 
language  was  finally  modified  by  the  different  races  who  had 
adapted  it,  to  Spanish,  French,  Portuguese,  and  Italian.  But 
the  Spanish  were  a  mixture  of  Keltic  and  Iberian  blood,  the 
French  were  of  Keltic  and  Gallic  stock,  and  the  Portuguese  of 
Keltic,  Gallic,  and  Iberian  descent.  Now  a  certain  amount  of 
Roman  blood  was  intermixed  with  all  these  peoples,  but  in 
hardly  an  instance  is  there  physically  a  race  characteristic  among 
them  that  is  distinctively  Roman.  A  similar  mixture  took  place 
in  the  case  of  the  English  people.  Although  popularly  known 
as  Anglo-Saxons,  the  amalgamation  is  far  more  extensive  ;  it  in- 
cludes Angles,  Saxons,  Jutes,  and  Danes,  together  with  a  general 
mixture  of  Gothic  blood.  To  this  must  also  be  added  the  infu- 
sion of  Latin  blood  that  came  with  the  Norman  Conquest. 

■*  The  Caucasians,  a  people  south  of  the  Caucasus  Mountains, 
who  are  usually  taken  as  the  best  type  of  the  white  races,  belong 
to  this  family. 

^  Among  the  various  races  of  Madagascar  the  Hovas  are  fore- 
most, and  in  respect  to  intellectual  development  are  not  surpassed 
by  any  other  African  peoples. 

^  In  spite  of  the  free  use  of  red  pigments  which  the  Indians 
were  accustomed  to  use  on  their  faces,  a  prevailing  characteristic 
of  the  race  is  the  color  of  the  skin,  Avhich  inclines  to  a  copper- 
red.  This  feature  is  not  true  of  the  Pacific-coast  Indians,  how- 
ever, all  of  whom  are  distinguished  by  swarthy  or  black-brown 
skins.  The  term  "red  men"  is  one  that  has  been  not  wisely 
chosen. 

'  Among  the  pre-historic  peoples  of  the  continent  none  have 
excited  more  interest  than  the  mound-builders  and  the  cliff- 
dwellers.  According  to  popular  belief  both  were  a  distinct  race 
of  people  whom  the  Indians  exterminated.  As  a  matter  of  fact, 
they  were  nothing  more  nor  less  than  Indians.  At  the  time  of 
the  discovery  of  America  by  Columbus,  some  of  the  native  Amer- 
icans, the  Aztecs  for  instance,  were  in  early  stages  of  civilization. 
Most  of  them,  however,  were  still  in  the  stone  age,  and  Avere 
therefore  in  a  state  not  higher  than  barbarism.      Still  others 


MAX  351 

were  in  an  intermediate  state,  and  tiiese  had  bey:un  to  forsake 
the  wickiup  or  tepe  for  houses  constructed  upon  architectural 
principles.  The  tribes  who  had  reached  this  development  were 
responsible  for  mound -building.  The  Senecas  and  Mohawks 
had  already  begun  to  build  the  famous  long  houses ;  the  Shaw- 
nees,  Cherokees,  and  Delawares  had  not  reached  quite  so  high  a 
plane,  and  were  still  mound-builders.  The  cliff-dwellers  were 
emerging  from  barbarism  and  built  their  pueblos  of  selected 
stone.  For  better  protection  they  commonly  built  them  on  high 
mesas,  on  cliflf-terraces,  or  even  in  caves.  The  Aztecs,  to  whom 
the  Zunis  and  Moquis  are  the  nearest  living  ai)proach,  were  on  a 
much  higher  plane  and  seem  to  have  emerged  from  barbarism 
at  the  time  of  the  conquest  of  Mexico. 

*'Some  of  the  Abyssinians  are  certainly  Semitic,  but  for  the 
greater  part  these  are  comprised  in  the  nomadic  Ai-abs  who  have 
gradually  extended  their  limits  to  a  large  part  of  Africa.  The 
earlier  inhabitants  are  Aryans,  however. 

'  The  existence  of  pygniy  tribes  is  mentioned  by  Herodotus, 
Pomponius  Mela,  Aristotle  and  others,  but  as  recently  as  thirty 
years  ago  it  was  believed  that  the  accounts  of  them  Avere  mythical. 
In  1865  the  famous  African  traveller,  Paul  Du  Chaillu,  dis- 
covered the  Obongo  tribe,  being  the  first  one  in  modern  times  to 
do  so.  His  accounts  were  flatly  contradicted  in  Europe,  Imt  u 
few  years  later  they  were  confirmed  by  Pfere  des  Avanchers,  an 
Abyssinian  missionary.  In  1871,  another  tribe,  the  Akka,  were 
discovered  by  Dr.  Scljweinfurth. 

•"It  is  by  no  means  certain  that  man  did  not  precede  the 
Glacial  epoch.  A  skull  found  by  Professor  Whitney  among 
Pliocene  deposits  and  various  other  relics  found  among  the 
auriferous  gravels  of  California,  indicate  a  nuich  greater  age  than 
post-glacial  exi.stence.  As  a  matter  of  fact,  the  search  for  pre- 
historic and  fossil  man  has  been  neither  extended  nor  systematic. 
Practically  no  investigations  have  been  made  amcng  the  .Miocene 
deposits  of  Central  and  Southern  Asisi,  when'  <>f  all  pla<es  sys- 
tematic researches  should  Ix?  made. 

"This  piece  is  now  in  the  British  Muwuin.  of  it>  origin  and 
antiquity  there  is  no  doubt. 

"The  Tartars  overran  Russia.  Turkey,  .umI  iliiidu^tan.  'I'liey 
are  among  the  most  intelligent  of  the  Turaiiie  peoples. 


CHAPTER  XX 

THE    INDUSTRIAL   REGIONS    OF    THE    UNITED    STATES 

The  main  body  of  the  United  States  extends  from  the 
colder  part  of  the  Temperate  Zone  to  the  Torrid  Zone, 
the  isotherm  forming  the  northern  boundary  of  the  latter, 
crossing  the  southern  parts  of  Florida,  Texas,  and  the 
lower  part  of  the  basin  of  the  Colorado  River.  This  part  of 
the  United  States  is  divided  naturally  into  physiographic 
regions  that  have  fairly  well-defined  boundaries ;  and 
because  of  their  features  of  surface  and  climate,  each  re- 
gion has  become  a  great  centre  of  industries  that  are  pe- 
culiar to  it. 

The  boundaries  of  these  regions  are  both  topographic 
and  climatic,  and  the  regions  themselves  differ  from  one 
another  in  either  climate  or  topography,  or  in  both. 
Roughly  speaking,  the  groups  of  States  commonly  recog- 
nized do  not  differ  very  greatly  from  the  industrial  groups 
that  result  from  diverse  conditions  of  climate  and  to- 
pography. 

The  following  are  the  principal  physiographic  and  in- 
dustrial regions  :  The  New  England  Plateau,  including 
the  eastern  part  of  New  York  ;  the  3Iiddle  Atlantic  States, 
including  the  Atlantic  Coast  Plain  and  the  middle  and 
southern  Appalachian  Highlands  ;  the  Great  Central  Plain, 
including  the  regions  commonly  known  as  the  Northern 
States  and  the  Southern  States ;  the  Western  Highlands, 
including  the  region  west  of  the  2,000-foot  contour,  the 
Rocky  Mountains,   the  Columbia  Plateau,  the  Colorado 

352 


35-i 


PHYSICAL   GEOGRAPHY 


Plateau,  the  Basin,  the  Sierra  Nevada  and  Cascade  Moun- 
tains ;  and  the  Pacific  Coast  Region.  Make  a  list  of  these, 
grouping  each  subdivision  under  its  principal  division. 

The  New  England  Plateau.— This  region  embraces 
the  northern  Appalachian  folds,  with  here  and  there  areas 
that  belong  to  the  Laui-entian  highlands.  During  the 
glacial  epoch  this  region  was  greatly  worn.  The  Appa- 
lachian folds  in  places  were  almost  obliterated,  and  the 


THE   RUGGED   SURFACE   AFFORDS   WATER-POWER 


Green,  White,  Adirondack,  and  Catskill  Mountains  are 
the  principal  remnants.  Here  and  there  are  isolated 
*'  monadnocks,"  most  of  w^hich  are  bosses  of  volcanic  rock 
which  were  able  to  withstand  the  erosion  and  corrosion 
that  resulted  from  the  work  of  the  ice  age.  Granitic  rocks 
prevail,  and  their  rounded  surfaces  are  generally  smooth 
and  polished. 

As  a  result  of  the  glacial  epoch  the  surface  of  the  New 
England  Plateau  is  very  rugged,   the  only  level  regions 


INDUSTKIAL  EEGIONS  OF  UNITED  STATES    355 

beiDg  the  river  flood  plains  and  the  old  lake  basins  Tvhose 
waters  have  disappeared.  Many  lakes  still  remain,  how- 
ever, and  these,  a  few  coast  lap;oons  excepted,  have  very 
strongly  the  character  of  glacial  lakes  and  tarns.  Name 
six  of  the  largest.  The  slope  is  somewhat  abrupt  and,  as 
a  result,  the  rivers  flow  in  "  reaches  "  ;  that  is,  stretches  of 
slack  water  alternate  with  rapids  and  falls. 

The  coast  region  is  equally  peculiar,  and,  inasmuch  as  it 
has  been  submerged  or  "drowned  "in  comparatively  re- 


A    HARBOR   COAST 


cent  geological  times,  the  sea  now  intrudes  upon  the  gla- 
ciated regions,  making  the  whole  shore  line  one  of  fjords, 
like  those  of  Norway.  Practically  all  the  good  harbors 
of  the  Atlantic  coast  of  the  United  States  are  confined  to 
this  region  and,  as  a  result,  about  four-fifths  of  the  foreign 
commerce  of  the  country  goes  in  and  out  of  its  ports. 


356  PHYSICAL   GEOGRAPHY 

The  rugged  surface  may  be  classified  as  uplands  and 
valley  lands.  The  uplands  are  characterized  by  thin  and 
innutritions  soil.  The  surface  is  diversified  by  drumlins, 
eskers,  and  granite  hog  backs ;  and  much  of  it  is  strewn 
with  erratic  bowlders.  The  uplands  are  not  capable  of 
supporting  a  dense  population/  and  in  the  past  half  cen- 
tury there  has  been  no  material  progress  in  agricultural 
pursuits  ;  on  the  contrary,  farming  lands  have  depreciated 
in  value.  About  all  the  industrial  gains  have  been  associ- 
ated with  manufacture.  How  does  the  surface  aifect  this 
industry  ?  The  farming  is  confined  to  the  lowland  valleys 
and  restricted  to  garden  and  dairy  products.  This  region 
is  celebrated  for  the  manufactures  that  require  a  high 
degree  of  intellectual  and  mechanical  skill,^  and  these 
have  resulted  from  the  conditions  that  have  afforded  the 
abundant  water-power.  The  manufactures  form  a  large 
proportion  of  the  nation's  foreign  exports.  The  sewing- 
machines,  bicycles,  clocks,  and  firearms  made  in  the  mills 
and  factories  of  this  region  are  shipped  to  almost  every 
part  of  the  world ;  the  cotton  cloth  is  used  by  about  every 
race  of  people. 

The  Middle  Atlantic  States. — This  region  includes 
the  principal  part  of  the  Atlantic  Coast  Plain,  together 
with  the  middle  and  southern  Appalachians.  The  lower 
part  of  the  Coast  Plain  consists  of  a  belt  of  swamp  lands 
bordered  by  sandy  pine-barrens.  Beyond  these  there  is  a 
belt  of  Piedmont  lands — the  foot-hills  of  the  Appalachian 
Mountains.  The  rivers  flow  into  estuaries  that  reach  usu- 
ally to  the  foot-hills  and  are  generally  navigable  to  this 
line — the  "  Fall  Line."  From  any  good  map  make  a  list  of 
cities  along  the  Fall  Line. 

The  soil  of  this  region  is  not  well  adapted  either  to  cot- 
ton or  wheat,  although  small  quantities  of  both  are  grown. 
The  chief  crops  are  early  fruit  and  garden  stuffs,  and  these 


INDUSTRIAL  REGIONS  OF  UNITED  STATES     357 

find  a  read}"  market  in  the  great  cities  of  the  manufactur- 
ing region.  Cotton  and  tobacco  are  important  crops  in 
the  southern  j^art  of  the  Piedmont  lands ;  and  on  account 
of  the  water-power,  noAV  tardily  developed,  the  manu- 
facture of  cotton  textiles  is  rapidly  becoming  the  leading 
industry.^ 

A  peculiar  feature  of  the  coast  is  noticeable  in  the  wave- 
formed  spits  or  barrier  beaches  of  this  region.     How  do 


COAL   GIVES   THK    POSSIBILITY    OF   MAKING   STtKL 


these  barrier  beaches  affect  commerce  ?  Explain  how  the 
barrier  beach,  with  the  enclosed  lagoon,  finally  becomes  a 
])art  of  the  Coast  Plain.  The  soil  of  these  beaches  pro- 
duces a  cotton  fibre  of  long  sta])le  and  great  strength,  an<l 
this  is  their  chief  i)roduct.  Tiie  fibre  is  used  in  lh(!  web 
of  bicvcle-tires. 


358 


PHYSICAL   GEOGRAPHY 


The  montane  part  of  this  section  is  low  and  not  very 
rugged  in  the  northern,  but  much  higher  in  the  southern 
part.  The  ApiJakichian  folds  contain  the  most  productive 
coal  measures  in  the  Avorld,  and  for  this  reason  they  are 
the  seat  of  extensive  iron  and  steel  manufactures. 

In  a  few  instances  the  iron  ore  occurs  in  the  vicinity  of 
the  coal  measures,  but  in  most  instances  cheap  transporta- 
tion by  water  enables  the  manufacturer  to  ship  the  ore  to 


THE   CHIEF   GRAIN    FIELD   OF   THE   WORI 


the  coal  mines  at  a  minimum  of  expense.  In  a  few  lo- 
calities, the  coal  shipped  by  canal  meets  the  iron  ore 
brought  in  steamers  and  barges  from  the  Lake  Superior 
iron  mines  to  the  shores  of  Lakes  Erie  and  Michigan,  and 
great  steel-making  plants  have  grow^n  up  at  Chicago,  Cleve- 
land, Lorain,  Toledo,  Ashtabula,  and  Buffido. 

From  the  foregoing  it  is  apparent  that  the  entire  Appa- 
lachian region,  both  folds  and  plateaus,  is  an  area  of  manu- 
facture because  of  certain  geographic  conditions,  and  these 


INDUSTRIAL  REGIONS  OF  UNITED  STATES    359 

are  the  existence  of  power.  The  waterfall  is  stored-up 
power  aud  so  also  is  the  coal.  The  power  within  the  coal 
not  only  makes  the  steam  that  drives  so  much  machinery, 
but  in  the  smelting  furnace  it  also  separates  the  iron  from 
the  ore ;  and  inasmuch  as  iron  aud  steel  form  the  basis  of 
most  manufactures,  the  existence  of  coal  implies  the  de- 
velopment of  a  great  centre  of  manufacture.'' 

The  Great  Central  Plain. — From  Hudson  Bay  to  the 
Gulf  of  Mexico  the  Great  Central  Plain  is  characterized  by 
a  level  or  a  gently  rolling  surface,  sloping  on  each  side 
toward  the  Mississippi  Eiver — the  whole  declining  gently 
from  a  slight  I'ise,  called  the  Heights  of  the  Land,  to  the 
Bay  on  the  north  and  the  Gulf  on  the  south.  Trace  the 
Heights  of  the  Land  on  the  map,  p.  353.  Within  what 
limit  of  elevation  is  the  greater  part  of  its  surface  ?  What 
is  the  general  elevation  west  of  the  Missouri  River  ? 

Most  of  the  rivers  flow  in  channels  that  are  from  one 
hundred  to  three  hundred  feet  lower  than  the  general  level 
of  the  land,  and  their  high  banks  are  the  bluffs  of  this  re- 
gion. For  the  greater  part  of  their  extent  the  bluffs  are 
not  less  than  one  or  two  miles  apart,  and  there  is  a  very 
level  flood  plain  between  them  —  the  famous  "  bottom 
lands."  All  through  the  Great  Central  Plain  the  soil  is 
naturally  very  fertile ;  that  of  the  bottom  lands  is  espe- 
cially productive. 

The  level  surface  and  the  general  conditions  of  topog- 
raphy make  this  region  one  of  sameness  so  far  as  external 
appearance  is  concerned.  Climatic  conditions,  however, 
make  two  separate  and  distinct  areas  of  history  and  indus- 
trv ;  therefore  it  is  divid(Ml  into  Northern  States  and 
Southern  States.  The  two  groups  are  roughly  separated 
by  a  boundary  formerly  known  as  "Mason  and  Dixon's 
line,"  and  tliis  boundary  in  former  years  was  siiarply  de- 
fined.    Incidentally    it    was    a    boundary    between    "  free 


360 


PHYSICAL   GEOGRAPHY 


States  "  and  "  slave  States,"  but  the  real  boundary  was  one 
that  separated  the  cotton-growing  region  from  that  in 
which  food-stuffs  and  manufactured  goods  were  the  staple 
products. 

In  the  Northern  States  wheat,  corn,  oats,  and  grass  have 
always  been  the  chief  products.  Because  of  the  level 
surface  and  the  deep,  nutritious  soil  the  grain  crops  can 


A   MODERN   HARVESTER 

//  could  not  be  used  in  a  rugged  country. 

be  both  planted  and  harvested  at  the  minimum  of  ex- 
pense. Under  no  other  conditions  of  topography  could 
there  have  been  such  a  wonderful  development  of  plant- 
ing and  harvesting  machinery.  As  a  result,  this  region 
has  become  one  of  the  principal  food-producing  regions  of 
the  world.  It  produces  one-fourth  of  the  Avorld's  crop  of 
wheat,  a  considerable  proportion  of  the  dairy  products, 
and  about  three-fourths  of  the  corn,  most  of  the  latter 
being  fed  to  hogs  and  converted  into  pork. 


INDUSTRIAL  REGIONS  OF  UNITED  STATES    361 

The  western  part  of  this  regiou — the  part  beyoud  the 
2000-foot  contour — does  not  receive  an  amount  of  raiu  suf- 
ficient to  mature  grain  ;  but  the  bunch  grass  and  the  al- 
falfa^ crops  are  the  food  of  great  herds  of  cattle.  As  a 
result,  the  Northern  States  of  the  Great  Central  Plain 
produce  the  flour  and  meat  not  only  for  the  United  States, 
but  much  of  that  required  by  the  rest  of  the  world. 

The  Southern  States  produce  about  four-fifths  of  the 
world's  supply  of  cotton.  Grain  can  be  grown  in  these 
States  but,  acre  for  acre,  the  crop  does  not  pay  nearly  so 
well  as  cotton;  and  cotton  cannot  be  grown  north  of  the 
line  that  separates  the  two  groups.  The  industries  and 
social  conditions — and,  therefore,  the  history — of  the  two 
sections  have  differed  greatly.  How  did  these  conditions 
encourage  slavery  in  the  one  group  and  discourage  it  in 
the  other  ? 

There  has  always  been  a  considerable  amount  of  man- 
ufacture in  both  sections,  but  the  manufactured  articles 
have  been  closely  related  to  the  grain  and  the  meat  prod- 
uct in  the  one  section,  and  to  cotton-growing  in  the  other. 
These  manufactures,  moreover,  have  been  greatly  en- 
couraged by  the  extensive  coal  measures  mainly  in  the 
northern  section.  Most  of  the  cotton  is  shipped  abroad, 
to  be  made  into  textiles  elscnvhere. 

The  Western  Highlands. — The  Western  Highlands 
embrace  all  that  region  between  the  eastern  foot  of  the 
Rocky,  and  the  western  foot  of  the  Sierra  Nevada  and 
Cascade  Ilanges.  This  region  is  characterized  1)}'  rugged- 
ness.  The  lofty  ranges  that  form  the  rims  of  the  high- 
laud  are  less  than  two  miles  in  altitude  in  few  places  t)nly. 
Fremont  and  South  Passes  are  the  chief  channels  of  in- 
tercommunication on  the  eastern  side.  On  the  west  the 
Central  Pacific  Puiilway  crosses  the  range  at  an  altitude 
of  nearly  10,000  feet.    In  the  north  the  canons  of  Columbia 


362 


PHYSICAL   GEOGRAPHY 


Eiver  and  its  tributaries  afford  grades  not  too  difficult  for 
railway  communication ;  on  the  south  the  canons  of  the 
Kio  Grande,  together  with  San  Gorgonio,  and  Tehachapi 
Passes — the  latter  at  the  southern  jimction  of  the  Sierra 
Nevada  and  Coast  Ranges — are  the  chief  routes  of  com- 
merce. 

The  ranges  of  the  Rocky  Mountains  are  lofty  folds  rest- 
ing each  on  a  core  of  trranitic  rocks.     The  Sierra  Nevada 


ImLr^kAi 


HAGERMANS   PASS 
The  ranges  and  canons  are  a  barrier  to  intercommunication. 


and  Cascade  Ranges  are  huge  blocks  of  tilted  rock  with  a 
gentle  slope  on  the  west  and  an  abrupt  escarpment  on  the 
east.  The  parallel  ridges  of  Nevada  and  Oregon,  com- 
monly called  the  "  Basin  Ranges,"  are  excelleut  examples 
of  block  mountains,  the  upturned  edge  of  the  block  con- 


INDUSTRIAL  REGIONS  OF  UNITED  STATES    363 

stitutiug  the  range.  Here  and  there  are  the  isolated 
knolls  that  form  the  laccolites  of  which  the  Henry  Moun- 
tains are  examples. 

The  western  slopes  of  the  Sierra  Nevada  and  Cascade 
Ranges  receive  a  generous  rainfall ;  consult  the  wind 
chart,  p.  221,  and  explain  why.  AVithin  the  rim  ranges 
the  rainfall  is  deficient.  In  the  northern  part  it  is  suf- 
ficient for  a  rather  scanty  pasturage,  but  the  southern  part, 
the  higher  plateaus  excepted,  is  a  desert. 

The  Columbia  Plateau,  or  "  Plains  of  the  Columbia,"  is 
mainly  the  surface  of  the  great  flood  of  lava  that  seems  to 
have  flowed  from  several  fissures  on  the  Sierra  Nevada 
Mountains,^  The  general  surface  of  the  plateau,  the  block 
ranges  excepted,  is  fairly  level,  but  the  region  has  been 
much  dissected  by  the  rivers,  whose  canons  are  from  five 
hundred  to  more  than  three  thousand  feet  deep. 

The  Colorado  Plateaus,  sometimes  called  the  "  Alcove 
Lands,"  consist  of  a  series  of  table-lands  varying  from  half 
a  mile  to  a  mile  and  a  half  in  altitude.  The  lower  plateaus 
are  desert  regions  of  tropical  temperature,  with  here  and 
there  a  few  tribes  of  squalid  Indians.  The  middle  plateaus 
have  suflicient  rain  for  a  very  scanty  covering  of  grass  ;  the 
higher  mesas  have  a  fair  growth  of  grass  and  timber. 

Canons  with  angular  outlines  and  almost  vertical  walls 
are  the  chief  characteristic  of  this  region.  The  canons  of 
the  Colorado,  which  have  made  the  region  famous,  in 
places  are  more  than  a  mile  deep.  Probably  nowhere  else 
on  the  face  of  the  earth  are  the  features  of  erosion  and  cor- 
rosion presented  on  such  a  stupendous  scale.  Every  mas- 
ter stream  and  every  tributary  is  practically  an  underground 
stream,  so  deep  are  their  chanm.'ls  below  the  general  level 
of  the  plateaus. 

The  Basin  Region  receives  its  name  from  the  fact  tliat 
none  of  its  drainage  reaches  the  sea.     On  the  slopes  of  the 


364  PHYSICAL  GEOGRAPHY 

block  ranges  tlie  rivers  are  vigorous  streams,  but  their 
waters  liually  disappear  by  evaporation  and  percolation  in 
the  sea  of  fine  rock  waste  at  their  bases.^  The  lakes  are 
without  outlet  to  the  sea,  and  most  of  them  are  the  shrunk- 
en remnants  of  two  great  lakes  that  once  covered  a  large 
part  of  this  region. 

One  of  these,  now  called  Lake  la  Hontan,  included  Hum- 
boldt, Pyramid,  Winnemucca,  and  several  other  lakes  ad- 
jacent. Several  of  them,  including  Walker  and  Owens 
Lakes,  have  never  wholly  disappeared  and  their  waters  are 
saturated  brines,  evaporation  continuing  until  the  water  can 
hold  no  more  saline  matter  in  solution.  Great  Salt,  Utah, 
Sevier,  and  Parowan  Lakes  are  the  remnants  of  former 
Lake  Bonneville  (p.  173).  Of  the  various  remnants  half  a 
dozen  have  wholly  disappeared,  and  Sevier  and  Parowan 
Lakes  are  practically  dry.  Utah  Lake  is  fresh ;  why  ? 
Great  Salt  Lake  at  present  is  shrinking  on  account  of  the 
diversion  of  its  feeders  for  purposes  of  irrigation.^ 

Two  small  areas  of  the  Basin  Kegion  are  below  sea-level. 
One  of  these,  Salton  Lake  and  its  basin,  are  undoubt- 
edly the  former  head  of  the  Gulf  of  California  ;  the  other. 
Death  Valley,  may  have  been.  The  "  sink  "  or  dry  bed  of 
Salton  Lake,  also  known  as  Coahuilla  Valley,  or  the  Sink 
of  San  Felipe,  was  most  likely  separated  from  the  present 
Gulf  by  the  sediments  brought  down  by  the  Colorado 
Eiver.  The  sediments  formed  a  bar  or  sea-wall  across  the 
Gulf  and  cut  it  in  twain.  The  upper  portion  in  places  has 
become  partly  filled  with  wind-blown  rock  Avaste,  but  its 
lowest  part  is  about  three  hundred  feet  below  sea-level. 
Death  Valley,  at  Kings  Springs,  is  nearly  two  hundred  and 
fifty  feet  below  mean  tide. 

Several  of  the  sinks  of  this  region  are  fed,  not  by  rivers 
that  normally  flow  into  them,  but  by  the  overflows  of  the 
Colorado  Kiver.     When   more   than   bank-full,  the  latter 


INDUSTKIAL  EEGIONS  OF  UNITED  STATES    365 

overflows  into  the  lower  land  to  the  westward.  Former 
Saltou  Lake  was  an  overflow  of  this  character.'  New  and 
Hardy's  Kivers,  frequently  chartered  on  maps  of  this  re- 
gion, are  not  streams  flowing  into  the  Colorado,  but  out  of 
it.  In  this  locality  the  river  practically  flows  around  the 
side  of  a  slope ;  and  at  times,  when  its  channel  is  choked 
with  sediment,  the  water  breaks  its  confining  bank  and 
temporarily  flows  out  into  the  desert. 


MOUNT    RAINIHR 
//  IS  the  ciiidcr-conc  of  an  extinct  volcano. 


The  climate  of  the  Basin  is  one  of  intense  heat,  and  the 
southern  part  is  tropical.  In  many  places  it  is  a  region 
of  dunes  swept  b}^  simoons,  and  occasionally  deluged 
by  cloudbursts.  To  the  latter  are  mainly  due  the  sinks 
and  washes  of  the  region.  Yuccas,  cacti,  mezquit  fa  spe- 
cies of  acaciaj,  and  gamma,  a  coarse  grass  resembling  the 
spinifex  of  Australia,  are  the  prevailing  vegetation  of  the 
southern  part ;  sage-brush,  a  kind  of  wormwood,  is  char- 
acteristic of  the  northern  region.     Wherever  irrigation  is 


366  PHYSICAL   GEOGRAPHY 

possible  the  soil  of  the  river  flood  plains  is  highly  pro- 
ductive, lu  the  southern  part  several  species  of  lizard, 
among  them  the  "  horned  toad,"  abound.  A  large  species, 
popularly  known  as  the  "  Gila  monster,"  inhabits  the  Gila 
River  and  is  peculiar  to  this  river  valley.  Herds  of  deer 
are  found  near  the  head  of  the  Gulf  of  Colorado ;  and  a 
few  camels,  the  descendants  of  imported  animals,"^  are  run- 
ning wild  along  the  lower  part  of  the  river. 

In  general,  the  conditions  of  both  climate  and  topogra- 
phy Avill  not  permit  the  Western  Highlands  to  become  a 
thickly  peopled  region.  The  rainfall  is  insufhcient  for 
the  production  of  food-stuffs,  and  the  latter  must  depend 
upon  irrigation  wherever  they  are  grown.  The  rugged 
surface  is  intensified  by  the  deep  and  precipitous  stream 
canons,  and  these  are  such  obstacles  that  commerce  is 
carried  on  only  at  an  enormous  expense.  In  one  or  two 
instances  a  canon  half  a  mile  in  width  forces  trafiic  to  make 
a  detour  of  several  hundred  miles  around.  The  mining 
of  copper,  lead,  and  the  precious  metals  is  the  most  im- 
portant industry. 

The  Pacific  Coast  Region. — This  region  includes 
the  western  foot-hills  of  the  Sierra  Nevada  and  Cascade 
Ranges,  the  Coast  Ranges,  and  the  great  intermontane 
valley  between  them.  The  principal  feature  of  this  re- 
gion is  the  distribution  of  rain.  During  the  winter  months 
the  moist  westerly  winds  are  sufficiently  chilled  to  shed  an 
abundance  of  rain  over  almost  the  entire  region.  Scarce- 
ly a  drop  falls  from  May  to  October.  The  rainfall,  there- 
fore, is  seasonal. 

The  foot-hill  region  is  more  or  less  rugged,  but  the 
greater  part  of  its  area  forms  excellent  ranges  for  cattle 
in  the  north,  sheep  in  the  south,  and  fruit  in  every  part. 
The  Coast  Ranges  lie  abruptly  against  the  shores  of  the 
Pacific   Ocean   and  in  only  a  few  places  is  there   even 


INDUSTRIAL  EEGIONS  OF  UNITED  STATES    367 


a  uarrow  coast  plain.  The  few  harbors,  however,  are 
deep,  commodious,  and  most  conveniently  situated.  In  a 
few  places,  however,  vessels  lie  alongside  a  high  cliff  and 
receive  their  cargoes  b}'  means  of  chutes  with  long  out- 
riggers. The  lower  ranges  of  these  mountains  form  ex- 
cellent pasturage  ;  the  river  valleys  produce  the  best 
"wheat  that  is  grown. 

The  great  intermontane  valley  is  probably  a  marine 
plain.  It  varies  from  twenty  to  about  one  hundred  miles 
iu  width,  but  in  sev- 
eral places  it  is  in- 
terrupted by  cross 
spurs  that  connect 
the  great  ranges. 
In  the  north,  Avliere 
it  opens  to  the  sea, 
it  is  known  as  the 
Sound  Y  a  1 1  e  y . 
What  strait  and 
sound  form  the  out- 
let ?  Farther  south 
the  Golden  Gate 
opens  from  the  sea 
into  one  of  the  prin- 
cipal harbors  of  the  world  ;  what  is  its  name '?  This  part  of 
the  intermontane  region  is  best  known  as  the  Sacrameuto- 
Sau  Joaquin  Valley. 

The  northern  and  southern  parts  of  the  intermontane 
valley  form  a  mammoth  wheat  field;  "  the  middle  portion 
consists  of  rolling  lands  that  form  excellent  cattle  and 
sheep  ranges,  and  furnish  the  possibilities  of  uidiinited 
water-power  not  yet  utili/iul.  South  of  Tehachapi  Pass  a 
fertile  lowland  lies  next  the  Pacific  which  yields  an  abun- 
dance of  semi  troi)ical  fruits  and  a  vcn-y  Hue  im'rino  wool. 


PATH   OF  A   SNOW 


368  PHYSICAL   GEOGRAPHY 

The  conditions  of  both  climate  and  topography  make  this 
a  region  that  is  capable  of  supporting  an  enormous  popu- 
lation. 

The  Territory  of  Alaska  forms  the  northern  part  of  the 
Pacific  Coast  region.  Its  climate  and  rugged  surface  ren- 
der it  unfit  for  all  agricultural  pursuits.  The  coast  slope 
is  moderately  warm,  but  the  rainy  season  is  about  ten 
months  in  duration  ;  the  interior  is  a  region  of  arctic 
temperature.  So  far  as  is  known  there  is  not  a  level  tract 
of  cultivable  land  large  enough  to  make  a  fair-sized  farm. 
The  chief  wealth  of  the  territory  is  contained  in  the  gold 
mines  of  the  Klondike  and  Cape  Nome  Districts  and  in 
the  fisheries  of  the  littoral  waters. 

The  Adjustment  of  Industrial  Pursuits  to  Environ- 
ment.— In  the  growth  and  development  of  a  nation  two 
processes  usually  are  going  on — the  acquisition  of  territory 
and  the  adjustment  of  the  pursuits  of  a  people  to  the  condi- 
tions of  their  geographic  surroundings.  The  latter  is  usu- 
ally attended  with  more  or  less  friction,  and  the  friction 
is  a  very  large  factor  in  their  history. 

In  the  geograjjliic  distribution  of  the  industries  of  the 
United  States,  one  may  follow  the  processes  of  adjustment. 
The  New  England  Plateau,  with  its  abundant  water-power — 
helped  also  by  steam-power — furnishes  the  country  with 
light  manufactures  and  textiles  and  exports  the  balance. 
The  people  of  the  harbor  region  carry  on  the  foreign  com- 
merce and  largely  control  the  great  railway  systems  that 
transport  the  manufacturer's  products  and  the  food-stuffs. 

The  people  of  the  Appalachian  region  manage  the  distri- 
bution of  the  coal  and  supply  the  country  Avith  steel  rails, 
bridge  material,  building  girders,  and  power-producing  ma- 
chinery. From  the  prairies  of  the  Great  Central  Plain 
come  the  breadstuffs  and  meat,  and  from  the  Atlantic 
Coast  Plain  the  fruit  and  vegetables  required  for  the  labor- 


370  PHYSICAL   GEOGRAPHY 

ers  in  the  crowded  mauufacturing  centres.  From  the  south 
comes  the  cotton  and  from  the  west  the  wool  that  is  to 
clothe  eighty  millions  of  people.  From  the  Western  High- 
lands are  obtained  the  gold  and  silver,  the  medium  of  com- 
mercial exchange,  and  much  of  the  copper  the  medium  by 
which  electric-power  is  transmitted.  Each  section  sup- 
plies not  only  the  rest  of  the  United  States,  but  a  large 
foreign  trade  as  well. 

In  (general,  the  area  which  produces  the  food-stuffs  and 
timber  means  great  population.  The  gold  and  silver  mean 
a  vast  commerce.  The  coal  and  the  iron  ore  are  forecasters 
of  tremendous  power. 

Natural  Resources.  —  No  other  nation  possesses  a 
greater  wealth  of  resources  than  the  United  States.  Some 
of  these  will  still  last  for  years,  but  others  are  nearly  ex- 
hausted. The  bison  and  the  fur-seal  are  practically  extinct, 
the  former  being  in  part  replaced  by  cattle  that  certainly 
are  of  greater  value. 

The  most  valuable  forest  trees  of  the  country  are  the 
pines.  Of  these,  a  belt  of  white  pine  extends  along  the 
northern  border ;  and  a  belt  of  yellow  pine  along  the  At- 
lantic and  Gulf  coasts.  Both  of  these  regions  are  nearly 
exhausted  of  their  supply  of  merchantable  timber.'^  The 
dense  forests  of  Douglas  fir,  or  "  Oregon  pine,"  and  red- 
wood of  the  Pacific  Coast  will  be  j)roductive  for  a  much 
gi'eater  length  of  time.  The  amount  of  growing  timber  is 
probably  greater  than  at  any  previous  time  in  the  history  of 
the  country,  but  most  of  it  is  not  adaptable  for  building  pur- 
poses. It  is  estimated  that  from  five  to  ten  million  young 
pines  are  destroyed  each  year  for  use  as  Christmas  trees. 

The  coat-Jields  cover  an  area  of  about  130,000  square 
miles.^-^  Of  the  amount  yielded  from  these  mines,  all  the 
anthracite  coal  comes  from  three  small  areas  in  Pennsyl- 
vania ;  these,  it  is  estimated,  will  be  exhausted  in  about 


INDUSTRIAL  REGIONS  OF  UNITED  STATES    371 

one  himdi-ed  years.  The  supply  of  bitumiuous  coal  is  prac- 
tically unlimited.  Much  of  the  coal-supply  is  used  as 
house  fuel,  but  by  far  the  greater  part  is  used  in  the  manu- 
facture of  iron  and  in  producing  steam. 

Coal  is  derived  from  woody  libre  that  in  time  i>ast  was 
subjected  to  heat  and  pressure  away  from  contact  with  the 
air.  Most  of  the  vegetable  matter  accumulated  in  the 
swamps  of  the  Carboniferous  Age.  The  coal  measures 
of  the  Pacific  Coast,  however,  are  of  much  more  recent 
origin,  and  formed  during  the  Tertiary  period. 

Petroleum,  or  rock  oil,  occurs  iu  various  places,  usually 


A    GATEWAY  OF  COMMERCE 

near  but  not  always  iu  the  coal-fields.  The  refined  oil  of 
commerce  is  shipped  to  almost  every  part  of  the  woild, 
aud  is  even  an  article  of  caravan  trade  in  Africa.  The 
principal  wells  of  the  United  States  are  in  AVestcin  Penn- 
sylvania, Eastern  Ohio,  and  West  Virginia.  There  is  also 
a  productive  region  in  Southern  California.  Natural  gas 
occurs  in  the  same  general  area,  but  the  gas  and  tlie  oil 
do  not  seem  to  be  associated.  The  gas  is  used  for  house 
fuel  and  for  making  steam.  The  supply,  much  of  which 
has  been  wasted,  is  becoming  exhausted. 

Iron  ore  occurs  in  ver}'  many  parts  of  the  L  uiLeil  States, 


372  PHYSICAL   GEOGRAPHY 

but  it  is  available  only  wlieu  it  can  be  shipped  to  places 
where  coal  is  cheaply  obtained.  The  Gogebic  and  Ke- 
weenaw deposits  on  Lake  Superior,  Iron  Mountain  in  Mis- 
souri, and  the  deposits  of  the  Appalachian  Mountains  are 
the  chief  supplies.  The  iron  is  obtained  from  the  ore  by 
smelting  the  latter  with  coal  or  coke.  The  "  pig-iron " 
resulting  is  then  converted  into  steel  ingots  by  the  Besse- 
mer process,  and  the  ingots  are  rolled  into  rails,  plates, 
and  billets,  and  other  structural  material. 

Gold  is  abundant  in  the  Western  Highlands.  It  is 
obtained  mainly  by  crushing  the  quartz  rock  in  which  it 
occurs  and  "  amalgamating "  or  dissolving  the  gold  in 
quicksilver,  or  by  the  use  of  other  solvents.  In  Alaska 
and  in  parts  of  California  most  of  the  gold  is  free,  being 
mingled  with  gravel.  It  is  obtained  by  "  washing "  the 
latter  away  with  water,  thereby  leaving  the  gold,  which  is 
much  heavier,  to  be  taken  up  by  the  quicksilver.  Silver 
also  occurs  in  the  Western  Highlands.  Copper  occurs  in 
the  Rocky  Mountains,  but  the  principal  part  of  the  prod- 
uct comes  from  the  Lake  Superior  region.  It  is  mainly 
used  for  tlie  transmission  of  electric  power.  One  of  the 
two  quicksilver-producing  regions  of  the  world  is  in  Cali- 
fornia and  this  state  yields  about  half  the  output. 

QUESTIONS  AND  EXERCISES.— Repeat  the  list  of  physiographic 
and  industrial  regions  enumerated  in  the  first  page  of  this  chapter. 

Why  is  the  New  England  Plateau  ill-adapted  to  grain-farming  ?  How 
does  topography  become  a  factor  in  the  economic  production  of  grain  ? 

State  the  various  ways  in  which  coal  is  used  as  power,  both  on  land 
and  at  sea. 

Study  the  furniture  and  equipments  of  the  school-room  and  make  a 
list  of  the  industries  there  represented.  Trace  the  geographic  source 
of  the  raw  material  employed  ;  where  is  each  manufactured  ? 

Explain  how  the  topography  of  the  northern  prairies  has  affected  the 
development  of  farming  machinery. 

Explain  why  cotton  growing  is  limited  to  its  present  latitude.     In 


INDUSTRIAL  REGIONS  OF  UNITED  STATES    373 

what  way  has  cotton-growing  affected  the  social  conditions  of  the  peo- 
ple of  the  Southern  States  ? 

Explain  how  and  why  the  topography  of  the  Western  Highlands  is  a 
barrier  to  commerce. 

Explain  how  and  why  the  geographic  distribution  of  industries  has 
resulted  in  the  enormous  development  of  railways. 

Describe  three  railway  routes  across  the  Continent ;  two  water  routes 
from  Chicago  to  tide  water. 

How  does  the  grade  of  a  railway  affect  the  cost  of  transporting  freight  ? 

Obtain  from  the  Hydrographic  Office,  Washington,  D.  C.,any  bulletin 
or  publication  explaining  the  kinds  and  uses  of  buoys  and  range  lights 
employed  in  harbors. 

Trace  the  course  of  a  deep  draught  steamship  entering  the  main 
channel  of  New  York  Harbor,  with  reference  to  the  range  lights.  {S^e 
map,  p.  j6g.) 

COLLATERAL   READING  AND   REFERENCE 

Powell. — Physiogi-aphy  of  the  United  States,  pp.  33-100. 

Davis.— Physiography  of  the  United  States,  pp.  2G9-304. 

McGrEE. — The  Piedmont  Plateau,  National  Geographic  Mag- 
azine, vii.,  261 . 

Hewes. — Statistical  Railway  Studies,  Amerii-aii  Raif/nii/s, 
pp.  42.5-449. 

NOTES 

'  There  has  been  a  constant  movement  of  people  from  the  up- 
land farms  either  to  the  cities  or  else  to  the  more  fertile  regions 
of  the  west. 

'  In  manufacturing  and  commercial  regions  there  is  a  greater 
amount /jer  ca/»/to  paid  for  education  and  higher  average  daily 
wages  than  in  any  otlier  part  of  the  country. 

'  By  manufacturing  the  cotton  in  the  region  where  it  is  grown 
there  is  .-^aved  the  transportation  of  the  cotton  from  the  field  to 
the  mills,  many  miles  distant. 

*The  United  States  now  leatls  in  the  manufacture  of  rails. 
Nearly  all  of  the  6,000  miles  of  steel  rails  that  span  Siberia  were 
made  in  the  rolling  mills  of  Pennsylvania. 

'Alfalfa  is  a  hardy  and  rapidly  growing  species,  very  closely 
related  to  clover.  It  is  fully  as  nutritious  as  clover  and  grows 
more  rapidly. 


374  PHYSICAL   GEOGRAPHY 

'  In  several  places  the  Columbia  River  has  cut  its  channel  deep 
into  the  flood  of  lava.  In  one  place  there  is  disclosed  a  forest 
which  was  overwhelmed  by  the  lava.  The  trees  are  felled,  but 
the  wood  is  in  a  good  state  of  preservation. 

'  At  times  the  beds  of  some  of  the  larger  streams,  such  as  Hum- 
boldt and  Carson  Rivers,  are  dry  in  the  day  but  contain  a  con- 
siderable amount  of  water  at  night,  when,  by  reason  of  lower  tem- 
perature, evaporation  is  lessened. 

°  On  the  whole  there  seems  to  be  a  slight  gain  in  the  volume  of 
the  lake.  Pyramid,  Carson,  and  Winnemucca  Lakes,  in  recent 
times  dry,  are  now  filling  up.  Their  waters  contain  not  much 
more  than  three  per  cent,  of  salt. 

*  At  the  time  of  the  last  filling  of  the  basin  the  water  was 
extremely  salt,  and  its  temperature  was  nearly  120"  F.  Because 
of  its  altitude — more  than  three  hundred  feet  lower  than  the 
Colorado  River — at  several  times  there  have  been  propositions  to 
turn  the  river  into  the  sink  and  thus  make  an  inland  sea. 
Evaporation  is  so  great,  however,  that  the  entire  volume  of  the 
Colorado  would  fill  but  a  small  part  of  the  basin,  nor  would 
there  be  any  outflow  from  the  sink  to  the  Gulf. 

'"  The  camels  were  first  imported  by  Jefferson  Davis,  at  the 
time  when  he  was  Secretary  of  War.  As  pack  animals  they  were 
successful.  A  camel  could  carry  twice  as  much  as  the  best  pack 
mule,  and  carry  it  twice  as  far  in  a  day.  The  pack  mules  and 
horses  were  in  mortal  terror  of  the  camel,  however,  and  the  rifle 
of  the  packer  in  time  put  an  end  to  the  experiment — and  prac- 
tically to  the  camel. 

"  The  excess  of  wheat  is  exported  mainly  to  Europe,  by  way 
of  Cape  Horn.  The  completion  of  the  Nicaragua  Canal  will 
bring  San  Francisco  nearer  to  London  than  its  rival  wheat  mar- 
ket, Calcutta,  now  is. 

'^  Forest  fires  probably  rank  first  in  the  destruction  of  timber. 
The  railways  make  the  heaviest  demand  on  the  oak,  which  is  em- 
ployed as  ties.  Between  the  railways  and  the  tanneries  the 
Pennsylvania  Appalachians  are  nearly  shorn  of  oak  and  hem- 
lock. The  paper-makers  also  use  an  enormous  amount  of  tim- 
ber in  the  manufacture  of  paper  pulp. 

■'Only  a  small  portion  of  this  area,  however,  is  productive. 
The  coal  measures  of  China  probably  surpass  those  of  the  United 
States. 


APPENDIX 


The  Elemexts  of  the  Solar  System 


Name. 

Distance  from 
Sun,  in  Miles;. •' 

Time  of 
Revolution. 

Diameter  in 
Miles. 

Number  of 
Satellites. 

Density 
Water=l 

Sun 

860,000 

2,992 

7,660 

7,918 

4,211 

20—300 

86,000 

70,500 

31,700'^ 

34,500-' 

1  4 

Mercury 

37,750,000 

66,750,000 

92,300.000 

141,000,000 

250,000,000 

480,000,000 

881,000,000 

1,771,000,000 

2,775,000,000 

88  days 
224    '^ 
365i-  " 

1.9  vrs. 

4.4''  '' 
11.8    " 
29.5    " 
84       " 
164     " 

6  8'' 

Venus * 

4  S'' 

Earth 

Mars 

Asteroids  .  .  . 

1 
2 

5.6 
4.2 

Jupiter 

Saturn  

Uranus 

Neptune  .... 

5 
9 
4 

1 

1.4 
0.7 
1.3- 

i.r^ 

'  The  periodic  time  of  the  asteroids  varies  from  3.1  years  to  7.8  years  ;  the  approximate 
average  is  4.4  years. 

'  These  values  are  approximate. 


II 

Deep  Borings 

The  following  are  the  greatest  artificial  depths  yet  obtained, 
that  at  Monongahela  probably  e.xtending  as  far  below  sea-level 
as  any  others.  The  two  deepest  borings  in  the  M'orld  were 
both  sunk  in  Germany,  at  Government  expense,  to  ascertain 
the  thickness  of  the  coal  measures,  and  also  whether  other 
beds  underlay  those  that  were  known.  The  deejx'r  of  the 
two  and  the  greatest  depth  yet  attained  is  in  the  coal-liclds  of 
Upper  Silesia,  at  the  little  mining  town  of  I'aruschowitz,  where 
tiie  diamond  drill   has  peucfnitcd  to  the  depth  of  G,r)7U  feet. 

375 


376  APPENDIX 

The  second  greatest  depth  is  that  at  Schladebach,  near  Leipsic, 
where  the  drill  was  sent  down  to  6,265  feet.  With  the  excep- 
tion of  the  borings  on  the  Monongahela  and  Wheeling  and 
the  deeper  of  the  two  wells  sunk  at  St.  Louis,  all  the  drilled 
holes  that  have  reached  an  exceptionally  great  depth  are  in 
Germany.     Here  is  a  list  of  the  deepest  bore-holes  ; 

Feet. 

Paruschowitz,  Upper  Silesia 6,570 

Schladebach,  near  Leipsic 6,265 

Monongahela  (thus  far  sunk) 5,532 

Wheeling,  W.  Va 4,920 

Sperenberg  (gypsum  beds  near  Berlin) 4,559 

Lieth,  near  Altona 4,388 

Eu,  near  Stassfurt 4,241 

Lubtheen,  in  Mecklenburg 3,949 

St.  Louis,  Mo 3,843 

Stennewitz,  near  Halle 3,644 

Inowrazlaw,  Posen 3,624 

Friedrichsaue,  near  Aschersleben 3,542 

Many  thousands  of  wells  have  been  sunk  in  this  country 
chiefly  in  the  search  for  petroleum  or  natural  gas,  but  most  of 
them  are  not  over  1,000  to  2,000  feet  deep.  The  greater  part 
of  the  artesian  wells  in  the  country  vary  from  200  to  1,000 
feet.  The  average  depth  of  the  many  thousands  of  artesian 
wells  sunk  for  irrigation  in  the  western  half  of  the  country  is 
not  far  from  210  feet. 

It  is  in  our  copper-mining  shafts  on  Lake  Superior  that  we 
take  first  rank  in  this  form  of  excavation.  Work  on  No. 
5  Tamarack  shaft  on  Houghton  Peninsula  began  in  1895,  and 
it  will  not  be  completed  until  1901,  when,  it  is  expected,  it 
will  be  the  deepest  shaft  in  the  world.  It  will  not  be  sunk 
to  a  greater  depth,  for  from  this  level  the  company  can  ob- 
tain all  the  ore  at  that  end  of  its  property.  There  is  but  little 
uniformity,  however,  in  the  rate  at  which  the  heat  increases  ; 
it  varies  from  one  degree  (F.)  in  fifty  to  one  in  every  seventy 
or  eighty  feet  of  descent.  In  some  cases  the  heat  is  due  in 
part  to  chemical  changes  in  the  rock. — C.  C.  Adams,  m  The 
New  York  Sun. 


APPENDIX 


377 


111 
Heights  of  Plateaus,  Ranges,  and  Peaks 


Plateaus 


Feet. 


Abyssinian 6,500—  7,500 

Allegheny    1,000—  1,500 

Australian 4,500—  5,500 

Bolivian 12,000—14,000 

Brazilian 2,800—  2,500 

Colorado 4,500—  6,000 

Columbia 4,000—  5,000 

Dekkan 2,000—  2,500 

Guiana 2,000—  3,000 


Feet. 


Heights  of  the  Land.    1,000—  1,500 

Iberian 2,000—  2,500 

Iran 5,000—  6,000 

Mexican  .      7,000 —  8,000 

Mongohan 3,000—  4,000 

New  England 1,000—  1,200 

The  "  Plains," 5,000—  6,000 

The  Pamirs 10,000—14,000 

Tibet 15,000—17,000 


Ranges 


Feet. 


Alps 7,000—  9,000 

Altai 6,000—  7,000 

Andes   12,000—15,000 

Apennines 3,500—  4,000 

Appalachian 1,500 —  2,500 

Atlas 8,000—10,000 

Balkan 4.000—  5,000 

Blue  (Oregon).   . . .   4,000—  4,500 

Carpathian 4,500—  6,000 

Cascade   7,500-10,000 

Caucasus 9,000—11,000 

Coast  (California)  .   2,500—  3,500 


Feet. 


Coast  (Canada) 4,500—  8,000 

Dragon  (So.   Africa).  4,000—  5,000 

Himalaya 16,000—19,000 

Hindu  kush 16,000—18,000 

Jura 2,500—  3,500 

Karakorum 18.000—19,000 

Ozark 1,200—  1.500 

Pyrenees   7,500—  9,000 

Rocky  (U.  S.) 6,000—  7,000 

"       (Canada) 9,000-10,000 

Tian  Shan 17,000—18.000 

Ural 2,000—  4,000 


Peaks 


Feet. 

Aconcagua  .23,900' 

Ararat 17,260 

Blanc 15,744- 

Ben  Nevis 4.368' 

Chimborazo  (volcano) 20.500 

Cotopaxi  (volcano) 16.300 

Dapsang   28, .3-10 

Demavend  (volcano) 18,800 

Etna  (volcano) 10,875" 

Elbruz 18,526' 

Everest 29,000'' 

Fremont  Peak   13,790 

'  Highest  in  South  America. 
»  Uiebest  in  Euroiie. 

•  nighest  in  Britifb  Islen. 

*  Highest  in  Caucasos. 


Feet. 


Fujiyama  (volcano) 14,177 

Hekla  (volcano) 5, 100 

Hood 11,900 

Kenia 18,000 

Kilima  Njaro 20,000" 

Kiiauea  (volcano)  Hawaiian 

Islands 4,00(1 

Logan 1!),50() 

Marcy,  New  York 5,467"* 

McKinley,  Alaska 20,4(;4' 

Manna  Kca   (volcano),  Ha- 
waiian Islands  14,000 

»  Posfibly  highest  in  the  world. 

"  IlighcHt  in  Adirondiicks. 

'  Proliably  highcpi  in  Norrh  .America. 

"  Possibly  highest  in  Alricii. 


Vanes  with  each  eruption. 


378 


APPENDIX 


Peaks  {Continued) 


Feet. 

Mauna  Loa  (volcano) 13,600 

Mitchell,  North  Carolina.. .    6,711' 
Hooker,  Britisli  Colnnibia..l5,700 

Orizaba  (volcano) 18,300- 

Pike's  Peak 14,147 

Popocatepetl  (volcano) ....  17,800 

Rainier  (Tacoraa) 14,441 

St.  Elias 18,024 

■  Highest  in  Appalachian  System. 

2  Highest  in  Mexico. 

»  PosBibly  highest  in  world  ;  not  surveyed. 


Feet. 


Shasta 14,440 

Sinai 8,600 

T.   45  (Himalayas) 29,100" 

Teneriffe 12,000 

Washington 6,286'* 

Whitney 14,898* 

Vesuvius  (volcano) 4,000" 

Wrangell 17,500 

*  Highest  in  White  Mountains. 

*  Highest  in  Sierra  Nevada  Range. 

*  Varies  with  each  eruption. 


IV 

Lengths  of  Rivers  and  Areas  of  their  Basins^ 


Miles. 

Amazon 4,000 

Amur   .2,500 

Brahmaputra 2,000 

Colorado 1,100 

Columbia 1,400 

Danube 1,800 

Dnieper 1,230 

Dwina 700 

Elbe 550 

Ganges 1,800 

Hoang 2,800 

Hudson 300 

Indus ...'..2,000 

Irawaddi 1,200 

Kongo   3,000 

La  Plata  2,300 

Lena 2,800 

Mackenzie 2,400 

Mekong 2,600 

Mississippi-Missouri. 4, 200 


Sq.  Miles. 
2,500,000 
750,000 
400,000 
230,000 
290,000 
300,000 
200,000 
150,000 
450,000 
450,000 
400,000 
13,000 
350,000 


1,500,000 

1,250,000 

750,000 

600,000 

300,000 

1,250,000 


Miles. 
Murray -Darling. .  1, 100 

Niger 3,000 

Nile 4,000 

Ob 2,800 

Orange 1,200 

Orinoco 1,500 

Po 450 

Rhine. 800 

Rhone 550 

Rio  Grande 1,800 

St.  Lawrence 2,100 

Sao  Francisco.  . .  1,800 

Seine   500 

Thames  215 

Tocantins- 1,000 

Volga 2,300 

Yangtze 3,100 

Yenesei 3,000 

Yukon 2,200 

Zambesi 1,800 


Sq.  Miles. 

350,000 

1,000,000 

1,250,000 

1,000,000 

275,000 

400,000 

27,000 

90,000 

35,000 

200,000 

560,000 

200,000 

23,000 

6,000 

250,000 

600,000 

700,000 

1,500,000 

400,000 

500,000 


1  Both  the  length  and  the  area  of  the  basin  are  approximate  except  in  a  few  instances ; 
the  length  of  almost  every  river  changes  from  year  to  year. 

2  Not  a  tributary  of  the  Amazon. 

It  is  well  to  bear  in  mind  that  the  length  of  a  river  is  apt  to 
vary  from  year  to  year,  partly  because  of  the  formation  of 
loops  and  cut-offs,  and  partly  owing  to  the  gradual  extension 
of  its  headwater  tributaries. 


APPENDIX 


379 


V 

Lakes 


Name. 


Area. 


Aral 

Assal    , 

Baikal 

Balkash  .... 

Caspian 

Chad 

Chapala 

Crater 

Dead  Sea. . . . 

Erie 

Great  Salt  . . . 

Huron 

Ladoga 

Michigan  .  . . 
Nicaragua .  . .  . 
Salton  Lake  '• . 

Superior 

Tanganyika  . . 

Titicaca 

Victoria 

Winnipeg. . . . 


Square  Miles. 

25,000- 

1,000' 

13,200 

8,500- 

170,000'^ 

10,0005 

1,300 


320 

573 

2,300-' 

23,800 

7,000 

22,450 

2,800 


31,200 
14,000' 
12,500 
26,000' 
9,400 


Depth. 


Altitude. 


Feet. 

200- 

200 

4,500 

135^ 

3,0002 

20^ 


2,300 
700" 
210 
50' 
734 
730 


320 


1,008 

1,200 

ttOO 


72 


Feet. 
50 
-580 
1,400 
1,000' 
-84 
1,000 
7,000 


-1,300 

9,960 

4,200 

581 

55 

581 

108 

-267 

602 

2,670 

12,500 

4,000 

710 


'  Approximate ;  the  figures  given  are  from  the  best  authorities,  but  vary  from  the 
measurements  of  others.  Lake  Assal  is  situated  in  a  depression  near  the  Gulf  of  Aden. 
It  is  the  head  of  a  small  bay  severed  from  the  sea  by  aeolian  sands.  It  is  fed  by  a  small 
stream  that  flows  from  the  sea  into  the  lake.  The  volume  of  the  lake  represents  the 
balance  between  inflow  and  evaporation. 

2  Subject  to  great  variations  ;  the  sign  —  prefixed  to  the  altitude  mdicates  below  sea 
level.    Salton  Lake  is  now  dry. 

VI 

The  Tides 
The  following  very  clear  solution  of  a  much  disputed  prob- 
lem is  given  by  Dr.  Emerson  E.  AVhite,  author  of  a  series  of 
mathematical  text-books.  It  is  only  proper  to  add  that  no 
theory  on  the  subject  fully  e.xpluins  all  the  phenomena  not('(l. 
Dr.  White's  solution  meets  the  views  of  nio.st  stmlents. 

Let  £■  equal  the  attraction  of  the  earth,  and  .1/ equal  the  attraction  of 
the  moon  <at  B,  and  M'  the  attraction  of  tin-  moon  at  A  and  C. 


380 


APPENDIX 


Since  distance  OB  is  less  than  OA  or  OC,  M>M'.  Hence  E~  M<B-  M', 
and  hence  the  water  at  B  is  lighter  than  at  A  or  C — i.e.,  has  less  specific 
gravity,  and  is  lifted  or  bulged  by  the  surrounding  heavier  water. 

Let  E  equal  attraction  of  the  earth  and  m  equal  attraction  of  moon  at 
B',  and  m'  equal  attraction  of  moon  at  A   or  C  .    Since  distance  OB'  is 


greater  than  OA'  or  OC,  m  <  m.  Hence  E  -v  m  <  E  +  m\  and  hence 
the  water  at  B  is  lighter  or  has  less  specific  gravity  than  at  A'  or  C  and  is 
lifted  or  bulged  by  the  surrounding  heavier  water.  Since  distance  OB  is 
less  than  OB',  M  >  m,  and  hence  the  tide  at  B  is  higher  than  at  B'. 


VII 

Table  Showing  the  Numbee  of  Grains  of  Moisture, 
BY  Weight  Necessary  to  Saturate  a  Cubic  Foot 
of  Air  at  Normal  Density. 


Temperature. 

Moisture  in 
One  Cubic 
Foot  of  Air. 

Temperature. 

Moisture  in 
One  Cubic 
Foot  of  Air. 

Temperature. 

Moisture  in 

One  Cubic 

Foot  of  Air. 

Degrees  F. 
-40 

Grains. 

.08 

Degrees  F. 
45 

Grains. 
3.42 

Degrees  F. 

68 

Grains. 

7.48 

-30 

.13 

50 

4.08 

70 

7.98 

-20 

.22 

52 

4.37 

72 

*8.51 

-10 

.36 

54 

4.69 

74 

9.07 

0 

.56 

56 

5.02 

76 

9.66 

10 

.87 

58 

5.37 

78 

10.28 

20 

1.32 

60 

5.75 

80 

10.94 

30 

a. 96 

62 

6.14 

90 

14.79 

35 

2.37 

64 

6.56 

100 

19.92 

40 

-2.85 

66 

7.01 

110 

26.43 

INDEX 


Ages,  geological,  3:> 

Altitude,  climatic  effects  of,  243 

Animals,  distribution  of,  223 

regions  of,  316 
Anticyclones,  249 
Artesian  wells.  i:i5 
Atmosphere,  21 

movements  of,  21G 
Asteroids,  17 
Atolls,  coral,  47 
Aurora  bo  ealis,  372 
Avalanches,  150.  I(j2,  103 
Axis,  effects  of  inclination  of,  14,  19 

Balance,  Nature's,  33 

Barriers,  310 

Basalt,  27 

Blizzards.  255 

Bores,  tidal,  200 

Breezes,  daj'  and  night,  219 

Brush  discharge,  272 

Camel.  39 

in  America,  -SoS 
Caverns,  142 
Climate,  changes  in,  290 

extremes  of,  292 

zones  of,  291 
Cloudbursts,  240 
Clouds,  234 

cirrus,  236 

cumulus,  236 

nimbus,  237 

stratus,  230 
Coal-fields  of  U.  S.,  370 
Coal  measures,  39 
Coast  forms,  51,  53 
CoM  waves,  254 
Comet,  Tempel'fi,  18 


Compass,  mariner's,  276,  286 

Continents,  42 

Coral  formations,  52,  54 

Coronas,  279 

Corrasion,  105 

Craters,  91 

Currents,  ocean,  200 

economy  of,  205 
Cyclones,  249 

tropical,  250 

winter,  252 

Degradation,  105 
Deltas,  115 
Deserts,  296 

distribution  of,  297 

winds  of,  223 
Development,  stages  of,  303 
Dew,  233 
Diffraction,  278 
Divides,  migration  of,  121 
Doldrums,  219 
Drift,  159,  200 
Drumlin,  159 

Earth,  curvature  of,  19 

dimensions  of,  13 

form  of,  12 

motions  of,  13 
Earthquakes,  cause  of,  98 

distribution,  99 

nature  of,  95 

phenomena  of,  98 
Eclij)tic,  plane  of,  14 
Electricity,  laws  of,  268,  282 
Environment,  3fi7 

adjustment  to.  30H 
E(|niiiiixcH,  preceKsion  of,  14 
Kriis,  geological,  32 


381 


383 


INDEX 


Eros,  17 

Erosion,  105 

Erratic  bowlders,  161 

Eruptions,  volcanic,  81 

Eskers,  160 

Eskimos,  340 

Estuaries,  1 1 5 

Evaporation,  latent  heat  of,  233 

Felspar,  26 

Floes,  193 

Flood-plains,  113 

Forestry,  distribution  of,  323 

Geoid,  12 
Geysers,  136 
Glacial  epoch,  35 
Glacial  ice  sheets,  155 
Glaciers,  153 

occurrence  of,  157 

physiographic  effects  of,  157 
Grain,  318 
Granite,  38  ^" 

HaU,  243 
Halos,  279 

Highlands,  western,  361 
Hornblende,  26 
Hydrosphere,  21 

Icebergs,  effect  of,  on  commerce,  161 

formation  of,  156 
Ice  of  the  sea,  193 
Ice-pack,  193 
Iron,  372 
Islands,  47 
Isobars,  260 
Isoclinals,  275 
Isogonics,  275 
Isotherms,  291 

Lagoon,  167 

Lakes,  accidental,  167 

geographical  distribution  of,  1 74 

glacial,  165 

marsh,  164 

physiographic  aspect  of,  ](;9 

playa,  169 


Lakes,  salt,  168 

walled,  185 
Land  storms,  252 
Life,  dispersal  of,  309 

nature  of,  303 

physiographical  aspect  of,  327 
Lightning,  283 
Lithosphere,  20 
Lode,  142 
Loess,  227 

Magnetic  pole,  274 

storms,  276 

variation,  274,  285 
Magnetism,  273 

laws  of,  273 
Man,  antiquity  of,  342 

migrations  of,  345 

races  of,  335 
Marshes,  176 

physiographic  aspect  of,  183 
Matter,  forms  of,  18 
Mediterraneans,  50 
Meteors,  18 
Mica,  27 
Mirages,  279 
Monsoons,  218 
Moraines,  154 

Mountain-ranges,  nature  of,  67 
Mountains,  distribution  of,  70 

economic  aspect  of,  72 

]ihysiographic  aspect  of,  69 
Movements  of  rock  envelope,  23 
Mud  volcanoes,  138 

Natural  resources  of  U.  S.,  370 
Neve,  153 
North  star,  14 

Oases,  297 

Ocean    waters,    physiographic    aspect 
of,  206 

Pacific  Coast  Region,  366 
Passes,  79 
Peat,  177 

Percolating  waters,  133 
Physiography,  man's  relation  to,  347 
of  under-ground  waters,  141 


INDEX 


383 


Plains,  distribution  of,  60-76 

economic  value  of,  61 

physiographic  aspect  of,  61 
Plants,  distribution  of,  315 

economic,  318 

regions  of,  316 

textiles,  322 
Plateau,  New  England,  354 
Plateaus,  distribution  of,  64,  78 

economic  aspect  of,  64 
Potential,  electric,  269,  282 
Pygmies,  333,  341 

Rainbows,  280 

Rainfall,  distribution  of,  238 
seasonal,  240 

Rainless  regions,  242 

Rapids,  119 

Rivers,  continental,  125 

economic  importance  of,  120 
geographical  distribution  of,  12:3 
growth  and  development  of,  110 
physiography  of,  107 

Rock  envelope,  21 
formation  of,  25 
waste,  movement  of,  183 

Rocks,  igneous,  27 
metamorphic,  30 
sedimentary,  27 

Sahara,  301 
St.  Elmo's  fire,  2T2 
Sandstone,  28 
Sand  valleys,  134 
Sandy  hooks,  207 
Sea,  48 

arms  of,  49 
Seas,  sargasso,  202 
Silica.  26 
Simoon,  223 
Sinter.  141 
Slate,  28 
Sludge,  193 
Snow,  243 


Solar  system,  9 
Sphagnum,  177 
Springs,  135 

mineral,  136 
Stalactites,  145 
Stalagmites,  145 
States,  Middle  Atlantic,  356 
Strata,  order  of,  30 
Sun  and  planets,  1 1 
Swamps,  176 

economic  value  of,  183 

lacustrme,  178 

Talus,  78 

Temperature,  extremes  of,  294 

mean  annual,  300 
Terraces,  115 
Thunder-storms,  271 
Tides,  195 
Tornadoes,  255 
Typhoons,  250 

Underground  streams,  139 
Unusual  adjustments,  122 

Valleys,  71 
Variation,  305 
Vesuvius,  eruption  of,  91 
Volcanoes,  nature  of,  85 

distribution  of,  89 
Vulcanism,  results  of,  86 

Water,  54 

envelope,  22 
Watershed,  127 
Waterspouts,  258 
Waves,  194 

Weather  forecasting,  259 
Wheat,  319 
White  squall,  57 
Winds,  216 

physiographic  effects  of,  224 

Zone  of  fracture,  54 


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